Knit Fabric Snagging Test

Knit fabric snagging is measured by ASTM D3939/D3939M (Mace Test Method), which rotates a tungsten-carbide-spiked mace at 600 revolutions per minute against a tubular specimen for 600 revolutions and rates the result on a 5-step photographic reference scale from 5 (no snagging) to 1 (very severe snagging).

A snag is a pulled yarn loop on the fabric surface created when a sharp or rough object catches a yarn and pulls it out of the structure, and knit fabrics are far more prone to snagging than most woven fabrics because the loop geometry lets a single snag pull an entire loop out of the construction. This article explains how the mace test works, which yarn and stitch variables drive the result, and how to read a snag rating when you are specifying knit fabric for apparel, hosiery, or upholstery.

Why knit fabrics snag more easily than wovens

Snagging is mechanically different from pilling and abrasion, even though all three live on the same family of surface-defect tests. Pilling rolls loose fibers into tiny balls on the surface; abrasion wears fibers down through friction; snagging pulls a yarn segment out of the fabric plane and exposes it as a loop or float on the face. The single defining feature of a snag is that the yarn has not broken; it has been pulled out of the fabric, often for several centimeters along the loop axis.

Knitted structures are more vulnerable to this mechanism for one structural reason: the yarn in a knit is held in place by loops that interlock with neighbouring loops through friction and yarn-on-yarn contact, not by tight warp-and-weft crossings as in a plain weave. When a hook or rough surface catches one yarn segment, the load transfers directly into the loop that holds it, and the loop can slide and elongate without breaking the yarn. In a tightly set plain weave, the same hook tends to break the yarn or push past it. That is why hosiery, single-jersey T-shirts, and warp-knit lingerie are flagged for snag risk, while dense cotton poplin in the same end use is rarely flagged.

Two fabric-level factors dominate snag behaviour in knits:

• Yarn type: smooth filament yarns (textured polyester, continuous-filament nylon) hide snags better than equivalent spun yarns because pulled filaments lie flat and reflect light uniformly, while spun-yarn ends bloom into visible pills.
• Loop length and stitch density: shorter loop length and higher courses-and-wales per centimeter give the loop more interlock neighbours, raising the force needed to pull it out of the plane.

ASTM D3939/D3939M Mace Test: how the test runs

The Mace Test is the most widely used snag-resistance method for knitted and woven apparel fabrics in North America. The published standard is ASTM D3939/D3939M, currently in the -21 revision. The principle is straightforward: a fabric tube is mounted on a rotating cylindrical drum inside a snag-testing chamber, and a mace (a ball studded with tungsten-carbide points) is allowed to bounce freely against the rotating tube for a fixed number of revolutions. The mace pins snag and pull loops out of the fabric surface; the specimen is then removed, relaxed, and rated.

The key parameters, taken directly from the published method:

• Specimen: a tube 165 mm wide by 330 mm long, sewn or folded and mounted on the drum.
• Mace weight: approximately 130 g, with tungsten-carbide points of defined geometry.
• Drum rotation: 600 rpm, equivalent to a relative surface speed of about 19 m/min at the test radius.
• Test duration: 600 revolutions (one minute), with optional extension to 1,200 or 2,400 revolutions for severe service.
• Conditioning: standard atmosphere of 20 °C ± 2 °C and 65% ± 2% relative humidity per ASTM D1776.

After the test cycle, the specimen is conditioned and rated against two reference scales:

1. Visual severity rating using the ASTM photographic reference scale, where 5 = no snagging and 1 = very severe snagging in half-step increments (5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1).
2. Snag count, where each distinct pulled loop or float on the face is counted manually and reported as number of snags per specimen.

Most knit-fabric specifications call for a rating of 3.5 or higher for general apparel, and 4.0 or higher for hosiery and sportswear where a single visible snag is a first-quality reject. A rating below 3.0 is generally considered unacceptable for first-quality apparel in the US market.

Other snag test methods: ICI, bean bag, pin

The mace test is not the only snag method in commercial use, and some European and UK laboratories still run historical methods that give meaningfully different numbers than ASTM D3939. The three methods worth knowing are:

• ICI Snag Tester (UK): a multi-pin rotating drum that catches yarns over a much larger fabric area. Tends to produce more numerous but smaller snags than the mace method, and is closer to real-world abrasion-plus-catch conditions in apparel.
• DuPont Bean Bag Test: a weighted bean bag rotates inside a fabric-lined cylinder. Used historically for automotive upholstery; gentler mechanism that better simulates snag-by-friction rather than snag-by-hook.
• Pin snag test: a row of sewing-machine needles is dragged across the fabric under controlled load. Used for inline quality checks in knitting mills, not for certification.

Numbers from these three methods do not transfer cleanly. A knit fabric rated 4.5 by ASTM D3939 might come out as 3.5 on the ICI tester or 5.0 on the bean bag method, and an apples-to-apples comparison is rarely meaningful without a known cross-calibration in the lab.

Yarn and stitch variables that change snag resistance

Within a single knit construction, four yarn and stitch variables explain most of the between-fabric variation you will see in a D3939 rating.

Filament vs spun yarn. A continuous-filament yarn has no protruding fiber ends, so when a hook catches the yarn and pulls a loop, the pulled segment lies flat and reflects light evenly. A spun yarn of the same count has surface fiber ends that bloom into pills once the yarn is disturbed, and the snag reads visually as a more obvious defect. For this reason, textured polyester and nylon filament yarns are the default choice for snag-sensitive end uses like women’s hosiery and microfiber sportswear.

Yarn linear density and filament count. Finer filaments (less than 1 denier per filament, in microfiber territory) resist snagging better than coarse filaments because the pulled loop is thinner and harder to see. Coarse monofilament yarns snag very visibly and are almost never used in knit apparel for that reason.

Heat-setting and yarn crimp. Heat-set textured yarns lock their crimp in place and resist loop distortion better than unset flat yarns. This is why texturized polyester (set yarn) is preferred over flat polyester for knit jersey that must pass a snag spec.

Stitch density and loop length. Tighter knits (more courses per cm and more wales per cm at a given yarn count) give each loop more interlock neighbours and raise the friction that resists pull-out. As a rule of thumb, raising stitch density by 10% improves the D3939 rating by roughly half a step on the 5-to-1 scale.

Reading a snag rating in a fabric spec sheet

A typical mill spec sheet will report ASTM D3939 results as a visual rating (e.g. “4.0”) plus a snag count (e.g. “3 snags per specimen”). Read both numbers, because they measure different failure modes: the rating captures how visible the snags are, while the count tells you how many discrete events happened. A fabric rated 4.5 with 12 snags has the same severity rating as a fabric rated 4.5 with 2 snags, but the second is generally preferred because there is less chance of a single severe snag in the final garment.

For first-quality knit apparel, use these benchmarks:

• Rating 4.5 or higher, snag count under 5: premium, suitable for high-end knitwear, sheer hosiery, and microfiber sportswear.
• Rating 3.5 to 4.5, snag count 5 to 15: acceptable for general apparel, casual knitwear, and most T-shirt end uses.
• Rating 3.0 to 3.5: borderline; usually acceptable for workwear or lined garments, often rejected for visible knit panels.
• Rating below 3.0: not first quality; suitable only for hidden panels, linings, or industrial end uses.

Practical application: hosiery, sportswear, upholstery

Snag resistance is rarely the headline spec for a fabric, but it is one of the most common reasons knit apparel is rejected on the inspection line. Three end uses carry the highest snag risk and benefit most from a documented D3939 rating.

Hosiery and sheer knitwear. Nylon hosiery was the original driver of the mace test in the 1960s, and the spec has not loosened. A snag in a 15-denier stocking is a return; the mill quality bar is typically rating 4.5 with no more than 1 snag per specimen on D3939.

Sportswear and microfiber knits. Polyester microfiber jersey and brushed-back fleece snag against Velcro, zippers, and fitness-equipment surfaces far more than against skin contact. Brushing the face, in particular, lifts filaments and reduces the rating by 0.5 to 1.0 step versus the same knit unbrushed.

Upholstery and automotive knit. Car seats and contract upholstery see repeated snag-and-pull from buckles, keys, and abrasive clothing. Bean bag and ICI ratings dominate this segment in Europe; ASTM D3939 ratings tend to come in 0.5 to 1.0 step lower because the mace is more aggressive than the in-service mechanism.

Frequently Asked Questions

What is the difference between snagging and pilling?

Snagging pulls a yarn segment out of the fabric plane as a loop or float without breaking the yarn, while pilling rolls loose fiber ends into small balls on the surface. A snag is a single discrete event that can often be pulled back into the fabric; a pill is an accumulation of broken fiber ends that must be trimmed or shaved off.

How many revolutions does the ASTM D3939 mace test run?

The standard test runs 600 revolutions at 600 rpm (one minute), but the method permits optional extensions to 1,200 or 2,400 revolutions for severe-service fabrics such as automotive upholstery or heavy workwear. Most knit apparel specs use the 600-revolution cycle and rely on the photographic rating scale from 5 (no snagging) to 1 (very severe snagging).

Which knit construction resists snagging best?

Tightly knitted warp-knit structures (tricot, raschel) resist snagging best among common knit types because each loop is held by multiple neighbouring loops along both the wale and course directions. Plain weft-knit jersey (single jersey) is the most snag-prone because every loop has only its direct neighbour to hold it in the fabric plane. Double-knit and interlock constructions fall between the two.

Can finishing treatments reduce snag severity?

Yes. Heat-setting locks filament crimp in place and improves snag ratings by roughly half a step on the D3939 scale; silicone or softener finishes can either help (by lubricating fibers so pulled loops lie flatter) or hurt (by reducing inter-yarn friction and letting loops pull out more easily). Brushing the face of a knit almost always worsens the snag rating by 0.5 to 1.0 step because it lifts surface filaments.

How do filament yarns compare to spun yarns in snag testing?

Smooth continuous-filament yarns (textured polyester, continuous-filament nylon) consistently out-perform equivalent-count spun yarns on D3939 because pulled filament loops lie flat on the surface and read visually as a soft shadow, while spun-yarn snags bloom into visible pills. Microfiber filament yarns (less than 1 denier per filament) extend this advantage further, which is why sheer hosiery and microfiber sportswear are almost always filament-knit constructions.

References

• ASTM International. ASTM D3939/D3939M-21 Standard Test Method for Snagging Resistance of Fabrics (Mace Test Method). astm.org — defines the mace geometry, drum speed (600 rpm), test duration (600 revolutions), and the 5-to-1 photographic rating scale.
• AATCC. Test Method 65, Snagging Resistance of Fabrics. aatcc.org — historical North American method covering the mace procedure and visual rating; cited alongside ASTM D3939 in current apparel specifications.
• ASTM International. ASTM D1776/D1776M-20 Standard Practice for Conditioning and Testing Textiles. astm.org — defines the 20 °C and 65% RH conditioning atmosphere used by D3939 and other textile surface tests.
• Booth, J.E. Principles of Textile Testing. Newnes (Butterworth-Heinemann) — textbook chapter on fabric surface-change tests covering snagging, pilling, and abrasion with reference fabrics and interlaboratory data.
• Saville, B.P. Physical Testing of Textiles. Woodhead Publishing (Elsevier) — chapter on objective measurement of fabric surface change, including detailed treatment of the mace method and ICI procedure.
• SGS Textile Testing Services. Snagging Resistance Test Method Overview. sgs.com — accredited test-lab description of the ASTM D3939 procedure, sample preparation, and rating scales used in commercial QC reports.

This article is the working reference for knit fabric snag testing under ASTM D3939 and related methods. Editorial by Iftay Khairul Alam, TextileTuts. Sources: ASTM D3939/D3939M-21, AATCC TM-65, ASTM D1776/D1776M-20, Booth (Newnes), Saville (Woodhead), SGS as cited.