A steel block has a thickness. A fabric has a thickness at a given pressure. Press a fleece lightly and it reads one value; press it harder and it reads a clearly lower one. Both readings are correct, and neither is useful unless you know how it was taken.
This is why thickness, the simplest-looking test in the laboratory, produces some of the most confusing comparisons between suppliers and buyers.
What defines a thickness measurement
Every textile thickness method fixes three things:
- The pressure applied by the presser foot.
- The area of the presser foot, which together with the load sets that pressure.
- The time between the foot touching the fabric and the reading being taken.
Change any one and you change the result, especially on bulky, napped or knitted fabrics. Woven shirting is relatively insensitive; terry, fleece, spacer fabrics and waddings are very sensitive.
ISO 5084
ISO 5084 is the general method for textiles and textile products. Its standard measurement uses a pressure of 1 kPa with a presser foot of 2000 mm² — a circular foot of about 50.5 mm diameter. The reading is taken after a fixed dwell time once the foot is resting on the specimen; follow the clause for the exact time.
Just as important is what ISO 5084 does not cover: textile floor coverings, nonwovens, geotextiles and coated fabrics. Each of those has its own method:
| Material | Thickness method |
|---|---|
| Woven and knitted fabrics, general textiles | ISO 5084 |
| Nonwovens | ISO 9073-2 |
| Textile floor coverings | ISO 1765 |
| Geotextiles | ISO 9863-1 |
| Rubber- or plastics-coated fabrics | ISO 2286-3 |
Measuring a needle-punched nonwoven to ISO 5084 is a common mistake. The result may even look reasonable, but it is not a result to the standard the buyer expects.
ASTM D1777
ASTM D1777 takes a different structure: it provides several options of presser foot and pressure, chosen according to the type of material. It does not give a single universal setting. Canadian practice has noted that the presser foot sizes required by the ISO standard do not agree with North American test equipment — a reminder that ISO and ASTM thickness values should not be compared directly unless foot and pressure happen to match.
When an ASTM D1777 thickness is specified, confirm which option, and set up the gauge to that option's foot and load before measuring.
Common gauge errors
The foot is dropped, not lowered. If the foot falls onto the fabric, its momentum compresses the specimen beyond the static pressure, and a compressible fabric does not fully recover within the dwell time. Good gauges lower the foot at a controlled speed. On manual dial gauges, train operators to lower the foot gently and consistently.
The reading is taken too early or too late. Bulky fabrics keep compressing for some time under load. Reading at five seconds instead of the specified time gives a higher value; leaving the foot for a minute gives a lower one. Use a timer, or a gauge that takes the reading automatically.
The specimen is too small. The specimen must extend beyond the foot on all sides. A specimen cut barely larger than the foot loses support at its edges and reads thinner.
The wrong foot is fitted. Gauges often come with interchangeable feet for different standards. A smaller foot with the same weight gives a higher pressure. Label the feet and the weights and record which combination was used.
Dirty or non-parallel surfaces. Fibre fly or a hair between the anvil and the foot adds to every reading. Clean both surfaces and zero the gauge before each series. Check periodically with a gauge block that the foot and anvil are parallel and the zero is stable.
Measuring at creases or selvages. Measure across the width, avoiding creases, folds and the selvage area, and take readings at several positions. Report the mean and the spread.
Conditioning matters more than people think
Fibre swelling with moisture changes thickness, and for some fabrics it changes compressibility as well. Condition specimens in the standard atmosphere of ISO 139 and measure in that atmosphere if you can. A fabric measured straight out of a warm, dry warehouse can read noticeably different from the same fabric conditioned.
Reporting thickness properly
A useful thickness result reads like this: "Thickness 1.84 mm (mean of 10), ISO 5084, 1 kPa, 2000 mm² presser foot." Any one of those items missing makes the figure hard to compare. In buyer specifications, insist that the method and pressure are written next to the limit.
Before you report
- Is the material within the scope of ISO 5084, or does it need ISO 9073-2, ISO 1765, ISO 9863-1 or ISO 2286-3?
- If ASTM D1777: which option?
- Correct foot and load fitted, and recorded?
- Foot lowered at a controlled speed, reading taken at the specified time?
- Specimen larger than the foot, away from creases and selvage?
- Gauge cleaned and zeroed; specimens conditioned?
Our benchtop thickness gauge reads to 0.01 mm over a 0.01–50 mm range with a 50.5 mm presser foot, and 5, 10 and 20 cm² feet are available as options. It is built in our own workshop in Istanbul, alongside portable and carpet versions.