The protective value of a firefighter's turnout fabric composite is found in the air that’s between the firefighter and the heat source. Air itself is the greatest single source of the insulative qualities in protective clothing. Best of all, it weighs nothing.
The way to achieve the best thermal protection is to use a multi-layer turnout fabric configuration in which each layer accomplishes part of the job. The thermal barrier systems have the most air spaces — they create the most layers of air and resist absorption to provide the most reliable thermal protection. Thermal barriers that use slippery yarns on the face cloth are also less likely to bind and resist a firefighter's movement.