Quick Answer
The ATPV (Arc Thermal Performance Value) of flame-resistant fabrics is mainly influenced by nine categories of factors: fiber composition and functional additives, fabric color, fabric basis weight, fabric construction, moisture and sweat, multilayer clothing systems and air gaps, base-layer material compatibility, laundering and service aging, and test conditions and system variability. No single parameter can independently predict ATPV. The final arc rating must be determined through formal open-arc testing of the relevant fabric or the actual multilayer system.
Based on our long-term production experience, formulation adjustments, and multiple batches of third-party arc testing, color and fabric construction are two of the most easily underestimated variables. When composition, basis weight, construction, and major finishing conditions are the same or similar, Navy Blue fabrics typically show ATPV values about 2-3 cal/cm² higher than red, orange, yellow, and other colors; at the same composition and basis weight, knitted structures typically show higher ATPV than woven structures, while satin weaves typically show higher ATPV than comparable twill weaves. These patterns can be used for R&D decisions and pre-test sample selection, but they cannot replace test reports for specific products.
What Is ATPV?
ATPV (Arc Thermal Performance Value) is a measurement used to evaluate the arc thermal protection capability of flame-resistant fabrics and protective clothing systems. It represents the incident energy level that results in a 50% probability of second-degree burn under standardized arc testing conditions.
However, ATPV is not determined by one single factor such as fabric weight or fiber content. Differences in fiber composition, fabric structure, color, moisture, layering and aging conditions can significantly influence the final tested value.
ATPV is typically determined through open-arc testing. Common test standards include ASTM F1959/F1959M and IEC 61482-1-1.[1][2]
For a complete explanation of ATPV definition, testing methods and Arc Rating requirements, see our ATPV Guide.
Understanding Safe-Guard Internal Test Data
The observations in this article regarding color, fabric construction, and certain formulation differences are based on our long-term production of flame-resistant fabrics, process adjustments, and records from multiple batches of third-party arc testing. They reflect engineering trends repeatedly observed under comparable conditions and are suitable for fabric R&D, test-sample selection, and technical communication with customers.
Because ATPV is also affected by variables such as yarn, thickness, density, dyes and auxiliaries, flame-resistant finishing, pretreatment methods, and test conditions, the empirical conclusions in this article should not be interpreted as fixed formulas applicable to all fabrics. Final product performance should still be based on formal test reports for the corresponding sample or actual clothing system.
9 Key Factors That Affect ATPV
1. Fiber Composition
Fiber composition determines the fundamental way a fabric responds to the high temperatures of an electric arc and is one of the basic factors affecting ATPV. Different fibers may carbonize, shrink, decompose, melt, or retain structural stability when exposed to heat. These responses directly affect the rate at which heat passes through the fabric and whether the fabric breaks open during testing.
From the perspective of flame-resistant mechanisms, arc-protective fabrics can generally be divided into the following categories:
Inherently Flame-Resistant Fibers
The heat resistance and flame resistance of fibers such as meta-aramid, para-aramid, and modacrylic are inherent in their molecular structures. At high temperatures, they generally do not melt and drip like ordinary thermoplastic fibers and typically provide good dimensional stability and structural integrity.
However, “inherently flame-resistant” does not necessarily mean a higher ATPV at the same basis weight. The main advantages of some aramid fabrics are high-temperature structural stability, heat resistance, and strength retention rather than the formation of a thicker insulating char layer.
Treated Flame Retardant Fibers
FR cotton, FR viscose, and similar fabrics obtain flame resistance through flame-resistant finishing. Taking durable FR cotton as an example, phosphorus-nitrogen flame-retardant systems can promote fiber dehydration and carbonization under heat, forming a char layer with a certain degree of thermal insulation and thereby slowing further heat transfer toward the inner side of the fabric.
Its final ATPV depends not only on the cotton fiber itself, but also on the flame-retardant chemistry, degree of fixation, finish add-on, char-forming efficiency, and laundering durability.
Blended Fiber Systems
Cotton/nylon blends, aramid blends, and blends of aramid with FR viscose are typically designed to balance multiple performance properties. For example:
- Cotton fibers can provide char formation and comfort;
- Nylon can improve abrasion resistance and tear strength;
- Meta-aramid provides heat resistance and dimensional stability;
- Para-aramid improves high-temperature strength and resistance to breakopen;
- FR viscose can improve moisture absorption and wearer comfort.
Therefore, changing the blend ratio affects not only flame resistance, but also fabric thickness, strength, breakopen behavior, and heat-transfer paths, ultimately changing ATPV or EBT.
2.Functional Additives
In addition to the base fibers, solution-dyed pigments, carbon particles, near-infrared absorbers, radiant-energy-reflective additives, and other functional auxiliaries may also alter how the fabric absorbs, reflects, and transmits arc-radiant energy.
Additives and optimized formulations can significantly change the ATPV of aramid fabrics. U.S. Patent US9598797B1 conducted a comparative test on aramid fabrics of the same basis weight: a standard fabric containing 93% meta-aramid, 5% para-aramid, and 2% antistatic fiber had a basis weight of 6.0 oz/yd² and an ATPV of 6.5 cal/cm²; at the same 6.0 oz/yd² basis weight, using aramid fibers containing internally and uniformly dispersed discrete carbon particles increased the ATPV to 8.9 cal/cm². In the example fabric, the total carbon-particle content contributed by the aramid fibers was only 0.4 wt%, and the patent explicitly excluded carbon in the antistatic fiber from that calculation. This comparison directly shows that discrete carbon particles specifically dispersed within aramid fibers can significantly increase ATPV without increasing fabric basis weight.[5]
3. Effect of Fabric Color on ATPV (Including Our Test Data)
Fabric color is not merely an appearance parameter; in the development of arc-protective fabrics, it may also have a significant effect on the final tested ATPV.
In actual arc testing, differences in Arc Rating can occur among different colors, with dark shades such as Navy Blue typically showing higher arc ratings than bright colors such as red, orange, and yellow. However, there is currently no simple mechanism that applies to all fibers and all fabric systems and can accurately explain this difference. Therefore, this phenomenon should not be attributed simply to a particular dye, dyeing process, or additive.
We have repeatedly observed a similar pattern in our long-term production and multiple batches of third-party arc testing.
Among comparable products with the same or similar fiber composition, basis weight, fabric construction, and flame-resistant finishing conditions, Navy Blue fabrics typically show ATPV values about 2-3 cal/cm² higher than red, orange, yellow, and other bright-colored fabrics.
This means that when the other major conditions are the same or similar, color itself should be treated as an independent engineering variable affecting ATPV. A target ATPV achieved by one color should not be assumed to apply automatically to other colors with the same composition, basis weight, and fabric construction.
During arc exposure, the fabric must withstand intense thermal radiation from the electric arc and undergo rapid heating, heat transfer, and material thermal response. Fabrics of different colors may differ in their absorption, reflection, and transmission of radiant energy, so the amount of heat ultimately transferred to the inner side of the fabric may also differ.
However, it must be emphasized that there is currently insufficient evidence to attribute the 2-3 cal/cm² difference observed in our testing precisely to any single optical or thermal mechanism.
Therefore, a more rigorous interpretation is:
The effect of color on ATPV has been repeatedly observed through actual arc testing, but the specific mechanism should not be oversimplified or directly equated with the effect of a particular dye or dyeing process.
At the same time, our test experience does not mean that every Navy Blue fabric will necessarily have an ATPV 2-3 cal/cm² higher than every red, orange, or yellow fabric. ATPV is still jointly affected by fiber composition, basis weight, actual thickness, fabric construction, flame-resistant finishing, fabric structure, and test variability.
The approximately 2-3 cal/cm² difference referred to here is an empirical difference repeatedly observed in our comparable samples and multiple batches of third-party testing under the same or similar major conditions. It is not a fixed conversion rule applicable to all flame-resistant fabrics.
Engineering Conclusion
For the development of arc-protective fabrics, color should not be treated as an insignificant appearance parameter.
If a particular Navy Blue fabric has already achieved the target ATPV, it cannot be directly assumed that a red, orange, or yellow fabric of the same specification will achieve exactly the same Arc Rating.
Especially when test results are close to category thresholds such as CAT 1 or CAT 2, a difference of 2-3 cal/cm² can be sufficient to affect whether the final product reaches the target protection category.
Therefore, in fabric R&D, color development, test-sample selection, and technical evaluation of products in different colors, color should be managed as an independent ATPV variable.
For final commercial colors, particularly products whose Arc Rating is close to the target category threshold, the most reliable approach remains formal arc testing of the actual fabric in the corresponding color rather than directly applying ATPV data from another color.
4. Fabric Basis Weight
Within the same fiber system and under similar construction and finishing conditions, increasing basis weight generally increases ATPV because there is more fiber mass per unit area, a longer heat-transfer path, and potentially greater actual thickness. However, this relationship is usually not strictly linear.
A higher basis weight cannot compensate for every formulation or structural limitation. A lightweight fabric optimized through fiber blending, construction, or additives may achieve a higher ATPV than an ordinary heavier fabric; conversely, two fabrics with the same basis weight may produce completely different test results because of differences in thickness, density, color, flame-resistant system, and breakopen behavior.
Therefore, basis weight is suitable for preliminary comparison within the same product family, but it should not be used to predict ATPV directly across different fiber systems. For internal product development, a useful engineering comparison metric is “arc-protection efficiency per unit basis weight”: achieving the target arc rating with the lowest practical basis weight while still meeting durability, strength, and comfort requirements.
5. Fabric Construction
Fabric construction changes effective thickness, surface coverage, pore structure, the amount of trapped still air, heat-transfer paths, and the way the fabric shrinks and breaks open when heated. Even when fiber composition and basis weight are the same, differences in fabric construction can produce significant differences in ATPV.
Our long-term production and multiple rounds of submitted-sample testing show that, under conditions of the same material and basis weight and similar yarn count and density, arc-protective knitted fabrics typically have higher ATPV than woven fabrics. The high-density knitted structures used in our products often provide greater surface coverage, greater effective thickness, and more trapped air between loops. Because still air has relatively low thermal conductivity, these structurally retained air layers slow heat transfer toward the inner side.
Among woven fabrics, our comparable samples typically show higher ATPV for satin weaves than for twill weaves. Satin weaves have longer floats and fewer interlacing points and, under similar yarn count, density, and basis weight, can generally form a more continuous, smooth, and compact surface coverage while also changing the heat-transfer path through the fabric and the material’s breakopen behavior.
This ranking is an engineering trend repeatedly observed within our current product systems. It does not mean that every knitted fabric will always have a higher ATPV than every woven fabric, or that every satin weave will always outperform every twill weave. Very open knitted structures, satin fabrics with insufficient thickness, or samples with major formulation and finishing differences may still break this trend.
6. Moisture and Sweat
When a fabric is completely saturated, its ATPV may decrease significantly. In a publicly available ArcWear report, a 7 oz/yd² 88/12 cotton/nylon fabric had an ATPV of 10.4 cal/cm² when dry; after full saturation with a 1% saline solution, its ATPV decreased to 5.5 cal/cm², a reduction of about 47%. After testing, the sample weight had increased by about 124%, indicating that this condition represented near-complete saturation rather than ordinary light perspiration.[6]
The reason is that water has a significantly higher thermal conductivity than still air. When the fabric absorbs water, some of the air originally present between fibers and yarns is replaced by liquid water, allowing heat to transfer more readily toward the inner side. Under high-energy exposure, rapid heating and vaporization of moisture may also increase the risk of thermal injury.
However, “slightly damp” and “fully saturated” conditions should not be treated as the same. The effect of normal perspiration on different materials and multilayer systems may be relatively small, or it may vary depending on moisture location, garment-to-body contact, and fabric construction. Field management should focus on visibly saturated garments: clothing fully soaked with sweat or rain should be replaced promptly; when work must be performed in rain, arc-rated rainwear should be used rather than ordinary non-arc-rated rainwear.
Recommendation: keep a dry FR shirt available on site and replace clothing promptly once it becomes fully soaked with sweat or rain. Wearing arc-rated rainwear in rainy conditions can indeed improve protection, but this only means that “wearing rainwear is better than not wearing it”; it does not mean that moisture itself poses no risk. Therefore, visibly saturated clothing should not be assumed to retain the same arc-protective performance as its dry-condition label rating.
7.Layering Effects
7.1Multilayer Clothing Systems and Air Gaps
The arc rating of a multilayer system cannot be calculated by directly adding the ATPV of each layer. In a publicly available Bulwark example, an FR base layer with an ATPV of 6.4 cal/cm² combined with a coverall rated at 9.0 cal/cm² achieved a tested system rating of 21 cal/cm², higher than the arithmetic sum of 15.4 cal/cm².[7]
This synergistic effect usually results from multiple mechanisms acting together: still air between layers increases thermal resistance; the outer layer absorbs energy, chars, or sheds material and thereby reduces the energy reaching the inner layer; and the distance and fit between inner and outer layers also affect the heat-transfer rate. The air gap is an important factor, but it is not the only one.
The additional protection is not guaranteed. e-Hazard explicitly notes that layering an 8 cal/cm² outer layer over a 4 cal/cm² inner layer does not automatically create a 12 cal/cm² system; only a system rating obtained through actual combination testing can be counted as protection.[8] Some combinations may produce substantial synergy, while others may provide little or no creditable gain, or may reach a limiting condition earlier because of outer-layer overheating, breakopen, or unfavorable layer-to-layer fit.
Therefore, multilayer systems must be tested as complete systems in the actual intended wearing order. If fabric sequence, garment ease, air gap, moisture condition, or base-layer material changes, the original system test result should not be applied directly.
7.2 Base-Layer Material Compatibility
An outer layer meeting the target ATPV does not mean that any garment worn underneath can be used safely. If the outer layer breaks open above its rating, or if a large amount of heat penetrates the outer layer, non-FR meltable synthetic materials may melt and adhere to the skin, causing additional injury.
Tyndale’s wearing guidance explicitly recommends avoiding ordinary polyester, nylon, and their non-FR blends as base layers. Options include wearing no additional base layer, using non-melting natural-fiber base layers such as 100% cotton, or using certified FR/AR base layers.[9] Although an ordinary cotton base layer is not prone to melting, it cannot automatically be counted toward the arc rating of a multilayer system; if its protection is to be credited, an FR/AR combination tested as a complete system is still required.
From the standpoint of predictability, FR-on-FR or AR-on-AR combinations are generally easier to establish as validated protective systems, provided that test data exist for the specific combination.
8. Laundering and Service Aging
An ATPV report reflects the performance of a specific sample under specified pretreatment and laboratory conditions. It does not mean that the fabric will maintain exactly the same arc-protective performance throughout its entire service life.
Laundering, ultraviolet exposure, mechanical abrasion, high temperature, and chemical contamination can all change fabric strength, thickness, char-forming capability, and structural integrity, thereby affecting actual protective performance.
The flame resistance of inherently FR fibers such as meta-aramid and para-aramid comes from the polymer structure itself, so normal laundering does not wash out the flame-resistant component in the way a surface coating might be removed. However, ultraviolet exposure, long-term thermal oxidation, repeated flexing, and abrasion can still reduce fiber strength, fabric integrity, and garment structural stability. Fading, yellowing, and strength loss may result from the same photo-oxidation process, but the degree of ATPV reduction cannot be inferred directly from color change alone.
Durable treated FR cotton and FR viscose should likewise not be described simply as having “flame retardant attached to the surface that washes off after a few cycles.” Mature durable flame-resistant systems typically form relatively stable flame-resistant structures within the fiber through chemical reactions and fixation processes. The relevant durability verification requirements of NFPA 2112:2023 specify testing of materials before and after 100 cycles under prescribed laundering or dry-cleaning conditions.[10] A fabric that passes this requirement must still meet the applicable performance requirements after the specified 100-cycle standard pretreatment.
One hundred cycles is a standardized verification point, not a universal retirement limit, and it does not mean the fabric fails immediately after the 101st laundering cycle. Beyond 100 cycles, whether performance is maintained depends on the specific flame-resistant system, laundering procedure, temperature, alkalinity, use of bleach and fabric softener, oil and chemical contamination, and whether the fabric has become thinned, torn, perforated, or damaged at the seams.
A more accurate management principle is to follow the manufacturer’s laundering instructions, avoid unauthorized chlorine bleach, oxidizing bleach, fabric softeners, and sizing agents, and evaluate replacement based on contamination, wear, and structural damage rather than using laundering count as the sole criterion.
Therefore, whether a garment remains suitable for use should not be judged only by the number of laundering cycles. It should also be evaluated against manufacturer requirements, contamination, wear, holes, thinning, and structural damage.
9. Test Conditions and System Variability
Open-arc testing itself has a certain degree of variability. Fabric lot, sampling location, warp/weft direction, conditioning state, pretreatment method, arc conditions, and sensor response can all affect the final data. ATPV is not derived from a single-point reading; it is determined by building a probability model from multiple exposure data points.
Therefore, slightly different results from two laboratories or two production lots do not necessarily mean that one result is incorrect. When comparing reports, confirm the test standard and version, laboratory, sample composition, color, basis weight, construction, number of layers, pretreatment method, test date, and whether the final result is reported as ATPV, EBT, or ELIM.
A test report answers the question, “How did this set of samples perform under these test conditions?” rather than, “Will every similar fabric always produce the same result?” If the color, formulation, basis weight, construction, or key finishing process of the same product changes, the need for retesting should be evaluated.
Comparison Table: 9 Factors Affecting ATPV
| Factor | Typical Effect | Key Consideration | Evidence Type |
| Fibers and Additives | May increase or decrease | Determine char formation, shrinkage, strength retention, and breakopen behavior; basic aramid fabrics do not necessarily have higher ATPV than FR cotton of a similar basis weight | Public product data + formulation mechanisms |
| Fabric Color | May cause significant change | In our comparable samples, Navy Blue typically shows ATPV about 2-3 cal/cm² higher than red and other colors | Multiple batches of our third-party test data |
| Basis Weight | Generally positively correlated | Within the same system, heavier fabrics generally show higher ATPV, but the relationship is not linear and cannot be used to predict across different fiber systems | Industry data + engineering experience |
| Fabric Construction | May cause significant change | In our samples of the same material and basis weight, knitted fabrics typically show higher ATPV than woven fabrics, and satin weaves higher than twill weaves | Multiple batches of our test data |
| Moisture and Sweat | Full saturation can significantly reduce ATPV | An 88/12 cotton/nylon fabric decreased from 10.4 to 5.5 cal/cm² after full saline saturation | Public ArcWear testing |
| Layering and Air Gaps | May produce synergy | A 6.4 and 9.0 combination tested at 21, but individual layer values cannot be added directly | Complete-system testing |
| Base-Layer Material | Incompatible materials may increase injury | Ordinary meltable synthetic base layers may melt and adhere; untested base layers cannot be credited toward the arc rating | Wearing guidance + system principles |
| Laundering and Aging | Generally unfavorable over the long term | NFPA 2112 uses 100 prescribed cycles as a durability verification point, not as a universal end-of-life limit | Standard requirements + use management |
| Test Conditions and Variability | Cause result variability | Standard version, pretreatment, sample direction, lot, and laboratory should be consistent when comparing results | Standardized test methods |
How Should Two Fabrics Be Compared for ATPV?
Comparing ATPV numbers alone can lead to incorrect conclusions. At a minimum, the following information should also be checked:
- Is the fiber composition the same?
- Are the basis weight, actual thickness, yarn count, density, and construction comparable?
- Is the fabric color the same?
- Are there differences in functional additives, solution-dyed components, or other additional formulation variables?
- Have the flame-resistant finish, softening finish, antistatic treatment, or other post-finishing processes changed?
- Is the sample a single-layer fabric, a material combination, or a complete garment?
- Are the laundering or dry-cleaning pretreatment methods and number of cycles the same?
- Is the test conducted according to ASTM F1959 or IEC 61482-1-1, and which specific version is used?
- Is the reported result ATPV, EBT, or ELIM?
- Are the test laboratory, test date, and sample lot clearly identified?
If the above conditions differ, the final numbers alone cannot be used to determine which fiber or which supplier is “better.” A valid comparison should control variables as much as possible, or directly test the specific samples intended for purchase from the same production lot.
Frequently Asked Questions (FAQ)
Q1: Does a higher ATPV always mean a better flame-resistant fabric?
Not necessarily. ATPV represents only arc-thermal protection. Actual fabric selection must also consider basis weight, comfort, strength, abrasion resistance, flame-resistant standards, and the specific hazard level.
Q2: Do fabrics with the same basis weight always have the same ATPV?
No. Differences in fiber formulation, thickness, construction, color, finishing, and breakopen behavior can result in significantly different ATPV values even at the same basis weight.
Q3: At a similar basis weight, does aramid always have a higher ATPV than FR cotton?
No. In publicly available Bulwark products, a Nomex IIIA fabric at approximately 255 g/m² has an ATPV of 6.7 cal/cm², while a 100% FR cotton fabric at approximately 235 g/m² has an ATPV of 7.7 cal/cm². This comparison shows that fiber category alone cannot predict ATPV, but it does not mean that all FR cotton fabrics have higher ATPV than all aramid fabrics.[3][4]
Q4: Does color really affect ATPV?
Yes. In our comparable samples with the same basis weight and material, Navy Blue typically shows ATPV values about 2-3 cal/cm² higher than red, orange, yellow, and other colors.
Q5: Does a knitted fabric always have a higher ATPV than a woven fabric?
In our arc-protective products with the same composition and basis weight and similar yarn count and density, knitted fabrics typically have higher ATPV than woven fabrics, mainly because of effective thickness, surface coverage, and trapped air layers. However, this is not an absolute rule that applies to every knitted and woven fabric; final performance still requires testing.
Q6: Can a fabric that is wet with sweat still be used according to its labeled ATPV?
Slight dampness and full saturation can have different effects. Publicly available testing shows that complete saline saturation can reduce the ATPV of some fabrics by nearly half. A visibly saturated garment should be replaced promptly and should not be assumed to retain its dry-condition label rating.
Q7: Can the ATPV values of multiple clothing layers be added directly?
No. Layering may sometimes produce a result higher than the simple arithmetic sum because of air gaps and material synergy, while in other cases there may be little or no creditable gain. Only the system rating obtained by testing the actual combination as a complete system can be used.
Q8: Does a fabric that complies with NFPA 2112 fail after 100 laundering cycles?
No. One hundred cycles is a standardized durability verification point. A compliant material must still meet the relevant requirements after the specified pretreatment. The 101st laundering cycle is not a universal failure point; actual service life depends on the fabric system, laundering method, contamination, wear, and garment damage.
Conclusion: ATPV Is the Result of Multiple Interacting Variables
ATPV cannot be calculated simply from “fiber name + basis weight.” Fibers and additives determine the fundamental thermal response; basis weight and construction determine effective thickness and heat-transfer paths; fabric color may affect the thermal response and final test performance under arc exposure; and moisture and air gaps in multilayer systems further alter performance under actual wearing conditions. Laundering, wear, and test conditions determine how broadly a particular report can be applied.
For fabric suppliers and garment manufacturers, a more reliable approach is to develop samples with controlled variables, record differences in color and finishing, select standards according to the target market, and formally validate the final commercial color, construction, or multilayer combination. ATPV data can guide material selection, but it cannot replace a site-specific arc-flash risk assessment and a complete PPE configuration.
If you are developing an arc-protective garment or sourcing FR fabric for a specific ATPV target, fabric selection should start with the actual application, required standard, target arc rating, basis weight, fiber composition, color, and garment structure rather than a single ATPV number.
Safe-Guard can support FR fabric development and sample selection based on your required specification, including Cotton FR, Cotton/Nylon FR, CVC FR, and antistatic FR fabric options. If you already have a target ATPV, fabric weight, color, or certification requirement, send us your project details so we can help evaluate suitable fabric directions before sampling and formal testing.
Need help selecting an FR fabric for a specific ATPV target? Contact Safe-Guard for sample development and technical support.
Sources and Notes
[1] ASTM F1959/F1959M-24b – Standard Test Method for Determining the Arc Rating of Materials for Clothing
[2] IEC 61482-1-1:2019 – Open Arc Test for ELIM, ATPV and EBT
[3] Bulwark – 7.5 oz Nomex IIIA, ATPV 6.7 cal/cm²
[4] Bulwark – 7 oz 100% Cotton Excel FR, ATPV 7.7 cal/cm²
[5] US9598797B1 – Carbon-containing arc-resistant aramid fabrics from dissimilar yarns
[6] ArcWear – Arc-Rated Clothing Evaluation of Sweat and Layering
[7] Bulwark – The Lowdown on FR/AR Layering
[8] e-Hazard – Are We Allowed to Layer Arc-Rated PPE?
[9] Tyndale – Base Layer Basics
[10] NFPA 2112 Public Standard-Development Document – 100-Cycle Laundering Requirement
