Thermoplastic cellular foam insulation performance is governed by the choice of resin, blowing agent composition, processing additives, and processing conditions. Thermal insulation performance benefits when the cellular voids comprising the foam contain a gas composition exhibiting thermal conductivity below that of air. Maintaining this gas composition is crucial to long-term thermal insulation performance. However, these gases will diffuse through the thermoplastic cell structure over time. Air will likewise diffuse into the cells. The result is an unfavorable increase in thermal conductivity over time. One means to reduce diffusion of gases is to reduce chain mobility via cross-linking. Bisazides such as diphenyl-4,4'-di(sulfonyl azide) can be used for generation of such a structure. The results reported herein demonstrate significant permeability reduction for industrially relevant blowing agents in films. Furthermore, compositions with low permeability have been tested to determine thermal conductivity after aging experiments.