ISO standards to determine the flammability of Lyocell fibers

Tencel (the brand name for Lyocell fibers produced by Lenzing) is a regenerated cellulosic fiber. Because it is chemically similar to cotton and rayon, it is inherently combustible and does not possess natural flame-retardant properties.

There is no specific ISO standard for Tencel. Instead, manufacturers and testing laboratories use internationally recognized ISO textile testing methods to evaluate the flammability characteristics of any cellulosic fabric. When testing a Tencel-based textile, the choice of standard depends entirely on the product’s intended end-use (e.g., apparel, workwear, or upholstery).

Primary ISO standards for flammability testing

These standards establish the protocols for measuring how a fabric behaves when exposed to a flame:

• ISO 6940 (Ease of Ignition): This standard measures how easily a fabric catches fire when subjected to a small, defined flame. It determines the minimum exposure time required to cause sustained ignition in a vertically oriented specimen.

• ISO 6941 (Flame Spread Properties): This method measures the rate and extent of flame propagation across the surface of a vertically oriented textile. It records parameters such as flaming time, non-flaming time, and the distance the flame travels, which are critical for assessing risk in apparel.

• ISO 15025 (Limited Flame Spread): This standard is widely used for protective clothing and workwear. It involves exposing a vertical fabric sample to a flame for a short period (typically 10 seconds). It records afterflame time, afterglow time, char length, and whether the material forms holes or produces flaming debris.

Factors affecting flammability

When conducting these tests on Tencel, the following variables will significantly influence the outcome:

• Fabric construction: Lightweight, brushed, or napped Tencel fabrics often exhibit faster flame spread due to higher surface area and increased oxygen availability. Denser, heavier weaves typically offer slightly more resistance than thin, sheer variants.

• Moisture content: Tencel is highly absorbent. Laboratory results are highly dependent on the ‘moisture regain’ of the fabric. Testing must be performed under controlled atmospheric conditions (typically 20°C and 65 per cent relative humidity, per ISO 139) to ensure consistent results, as bone-dry Tencel will ignite much faster than conditioned Tencel.

• Chemical treatments: Because Tencel is not inherently flame-resistant, any garment or textile required to meet specific fire safety codes (e.g., for curtains or high-risk industrial clothing) must be treated with appropriate flame-retardant (FR) chemicals and tested against the relevant standard for that application.

Important distinction

It is essential to distinguish between fiber production certifications and flammability test standards:

• Lenzing’s certifications (e.g., ISO 9001, ISO 14001): These refer to the quality, environmental, and safety management systems of the fiber manufacturing process. They do not imply that the fiber is flame-retardant.

• Flammability standards: These are performance tests. If you are conducting compliance testing for a commercial product, you must select the standard mandated by the safety regulations for your specific market (e.g., children’s sleepwear, public-use curtains, or industrial PPE), as the ‘pass/fail’ criteria are defined by those regional regulations rather than by the fiber type itself.