Air Layers and Thermal Barriers

The protective value of the fabric composite is really found in the air that’s between the fire fighter and the heat source. Air itself is the greatest single source of the insulative qualities in protective clothing. Best of all, it weighs nothing and it’s free! The most functional way to achieve the best protection is to use a multi-layer configuration in which each layer accomplishes part of the job. Extremely efficient insulation can be gained by creating very thin air spaces between the layers, which supplement the air contained within the layers. It’s important that none of these individual air spaces exceed 1.8 cm of thickness, because convective currents start beyond that thickness and may begin to quickly transmit heat. Similarly, air layers that are replaced by water can be unpredictably dangerous. Unlike air, water is an amazing conductor of heat.

It is logical that the thermal barrier systems which have the most air spaces can create the most layers of air or can resist absorption (water replacement of the insulating air) will provide the most reliable protection.

Another important consideration for thermal barriers relates to comfort and mobility. It is now widely recognized that thermal barriers which use slippery yarns on the “face cloth” next to the wearer are far less likely to bind and restrict the fire fighter’s movement. The super-strong filament yarns which create this lubricity are also excellent at wicking perspiration away from the body. (read more)