Intended mainly to measure the water-repellent efficacy of finishes, TM 70, Water Repellency, Tumble Jar Dynamic Absorption Test is not intended to predict rain penetration resistance.⁴ Specimens are tumbled in water, weighed, and the wet weight is compared to the dry weight.

Water Resistant

AATCC TM 35, Water Resistance: Rain Test and TM 42, Water Resistance: Impact Penetration Test use the weight of the water penetrating the fabric as a measure of resistance. Less than 1 g is usually considered acceptable;³ anything over 5 g is reported as > 5 g and indicates failure as a water-resistant fabric.² The rain test may be performed at different pressures to simulate different intensities of rain and acceptable ＆#118alues for both tests may vary according to end-use.

Another measure of water resistance is TM 127, Water Resistance: Hydrostatic Pressure Test. Water is directed at one side of the fabric under increasing pressure and the point at which water droplets appear on the opposite side is recorded. This test differentiates between the water resistance of the fabric and the water repellency of the fiber, yarn, and fabric construction. The degree to which the fibers and yarns resist wetting, combined with the size, shape, and number of pores in the fabric construction, influences the overall penetrability of the fabric.⁵

Weather Resistant

Weather resistance, the ability of a material to resist degradation of its properties when exposed to climactic conditions,⁶ is an even more complicated issue. AATCC TM 186, Weather Resistance: UV Light and Moisture Exposure subjects fabrics to artificial weathering through the use of ultraviolet (UV) light, humidity, and/or water spray. Exposed fabrics are compared to control fabrics in terms of color change and breaking or bursting strength. This test is most appropriate for items which will be placed outdoors for extended periods of time. The test method suggests three cycle options based on end-use梘eneral applications (e.g., outdoor furniture fabrics, and tent material), architectural applications where thermal shock may be an issue, and automotive exteriors. The UV and humidity/spray conditions for each application vary slightly. TMs 111, 169, and 192 are similar tests, using different combinations of light and/or water to simulate weathering.

So, will your fabric keep you dry?

Waterproof fabric will protect you from rain, but will eventually make you hot and sweaty. A water-repellent fabric will probably keep you dry if you are out in the rain for just a few minutes. Water-resistant fabrics may also keep you dry temporarily and they will be more breathable than waterproof fabrics, but water will eventually soak in, making the fabric heavy and wet. While a weather-resistant fabric makes no promise to keep you dry, it will continue to look and perform as it was intended even after prolonged exposure to sun and rain.

References

 1. Dictionary of Fiber & Textile Technology, KoSa, Charlotte, N.C., U.S.A., 1999, p215.

 2. AATCC Technical Manual, Vol. 81, 2006, pp65-67, 85-88.

 3. Annual Book of ASTM Standards, Vol. 7.02, West Conshohocken, Pa., U.S.A., 2005, p992.

 4. AATCC Technical Manual, Vol. 81, 2006, pp99-100.

 5. AATCC Technical Manual, Vol. 81, 2006, pp211-212.

 6. AATCC Technical Manual, Vol. 81, 2006, pp348-352.

Note: Story by Diana Wyman, AATCC.