Stretch denim that bags at the knee by lunchtime. Leggings that are loose at the waist after a day. Swimwear that has lost its shape after a season. None of these are strength failures; they are failures of growth — the length a fabric keeps after it has been stretched and released.
Two ASTM methods dominate this area for apparel fabrics, and they are not interchangeable.
Three properties, not one
- Fabric stretch — how much the fabric extends under a specified tension, measured while the tension is applied.
- Fabric growth — how much longer the fabric remains after the tension or extension is removed, measured after a stated recovery time.
- Fabric recovery — the share of the extension that the fabric recovers.
A fabric can stretch generously and still grow badly. Specifications that ask only for "stretch %" miss the property consumers complain about.
ASTM D2594: knitted fabrics with low power
ASTM D2594 covers fabric stretch and fabric growth of knitted fabrics intended for low-power stretch applications. It is explicitly not for fabrics meant for support or other high-power uses. The method is a hanging-load test: a looped specimen with bench marks is stretched by a hanger assembly and weights or a tensiometer, and the bench marks are measured with a light rule.
The method separates two end uses, and they are tested under different conditions:
- Loose-fitting apparel ("comfort stretch") — sportswear and similar.
- Form-fitting apparel ("semi-support") — swimwear, anchored slacks and other close-fitting garments.
In the 2004 edition, for example, growth was measured by holding the loop at a set percentage extension (different for wale and course direction, and for each end-use class) for two hours, then measuring after 60 seconds and after one hour of recovery. Stretch was measured under a 5 lbf or 10 lbf tension after four exercise cycles, depending on end use. The method has since been revised (a 2020 edition is listed), so check the current text for the exact values.
One sentence in the 2004 edition deserves attention: the method was not recommended for acceptance testing of commercial shipments, because its between-laboratory precision was known to be poor. If you are using D2594 results to accept or reject deliveries, agree the procedure and a comparison test with your supplier first.
ASTM D3107: fabrics woven from stretch yarns
ASTM D3107 covers stretch, growth and recovery of fabrics woven wholly or partly from stretch yarns. In its 2003 edition it targets woven fabrics with high stretch (more than 12 %) and good recovery from low tension, and offers two tension options commonly used in industry: 1.35 kg (3 lb) and 1.8 kg (4 lb).
D3107 measures growth in more than one way — after a specified tension, and after holding the specimen at a specified extension — and at several recovery times, from seconds up to two hours. It is not a breaking-elongation test; that belongs to the strip tensile method.
Trap 1: the wrong method for the construction
A stretch knit tested to D3107, or a stretch woven to D2594, produces a number that no specification is written for. Check the construction and end use before choosing. For high-power support fabrics, D2594 itself refers you to other methods.
Trap 2: the wrong end-use class
In D2594 the loose-fitting and form-fitting conditions use different extensions and tensions. The same fabric tested under the two conditions gives two different growth figures, both correct. If the intended end use is not known, the 2004 edition suggests testing under both. Always report which was used.
Trap 3: the recovery time is missing
Growth falls as the fabric rests. A growth figure measured 60 seconds after release and one measured an hour later describe the same fabric at two moments; neither is "the" growth. A report that says "growth 6 %" without a recovery time cannot be compared with anything. Report every interval the method requires, with its time.
Trap 4: uncontrolled timing and handling
Stretch tests are timed: how long the specimen is held extended, how long each exercise cycle takes, when the reading is taken. A timer per station, not a wall clock, keeps these consistent when several specimens are running. Handle specimens gently between steps — pulling a loop straight to "help" it settle is an unrecorded extra cycle.
Trap 5: unconditioned specimens and weights nobody checked
Both methods test in the standard atmosphere for textiles (ASTM D1776). Elastane and nylon blends respond to moisture and temperature. Weights and tensiometers are measuring instruments; include them in calibration, and keep the sets for different methods physically separate.
Hanging weights or a tensile tester?
European practice often uses EN 14704-1, a strip test for fabric elasticity carried out on a tensile testing machine with repeated loading cycles. Results from a cyclic tensile test and from a static hanging-load test are not interchangeable even when the numbers look similar. Choose the method the specification names.
Our multi-station stretch and recovery tester runs several specimens at once with a separate timer for each station, in 3- or 6-station versions, with weight sets chosen to suit the method you apply. It and our fabric extensometer, supplied with a marking template, are made in our own workshop in Istanbul.