There is currently significant development of sun protective clothing by the garment industry and concurrent development of textile chemical processes to enhance the UV absorption of garment textiles. The need to establish test methods and performance standards for this developing area has resulted in the establishment of a sun protective clothing category in ASTM Subcommittee D-13, Textiles and a similar work group in AATCC Committee RA-106. However, in our own investigations in this field it became evident that the thermal character of the garment or textile treated to enhance the UV absorption varied greatly depending upon a number of factors.
The thermodynamic behavior of the garment has significant impact on clothing comfort and human solar heat load. This paper describes methods developed by the author with guidance from personnel at the US Army Research Institute for Environmental Medicine (USARIEM) in Natick, MA and carried out at Atlas/DSET Laboratories in Phoenix, AZ.
The first method comparatively determines the total solar radiation (TSR) transmitted through two textile samples using small pyranometers. A secondary experiment measuring relative microclimate humidity, incorporates a Vaisala Instruments humidity sensor and 120 cc's of water placed inside the enclosed box to simulate perspiration.
The second method, incorporating smaller fabric sample sizes and smaller, non-conducting boxes, uses thermocouples placed on the under-surface of the fabric enclosing the small box. A second thermocouple probe situated in the approximate one-inch enclosure space in the box, provides a measure of the ambient air temperature of the samples under consideration.
A third method, infra red thermometry, provides the most dramatic, visual demonstration of the comparative thermodynamic behavior of fabrics or garments. In our investigations, an IR ThermaCam®, manufactured by Inframmetrics, Inc. of Boston, MA. was used to digitize andstore calibrated, pseudo-color thermal images of fabric samples and human subjects during solar exposure trials.
Together, these three methods adequately characterize the behavior of sun-protective clothing and permit a full assessment of the possible physiological costs and benefits of various methods, chemical processes, etc. of creating sun protective clothing.