Garments made of DuPont™ Nomex® brand fiber provide outstanding, built-in flame resistance. However, applying flammable contaminants to these, or any flame-resistant (FR) garments, will reduce the thermal protection and is never recommended.
Some insect repellents, including those with N,N-diethyl-M-toluamide (DEET) and Picaridin are flammable contaminants. Treating FR fabrics with DEET and Picaridin will impact their flammability and should be avoided.
In 2005 the U.S. Forest Service studied the impact of DEET and other insect repellents on their FR clothing. Based on the number of wildland firefighters outfitted, they studied Nomex® fabrics and concluded that DEET negatively impacted the flame resistance of Nomex® fabrics. For further information, refer to the USDA Forest Service July 2005 Tech Tips.