Improved insulation is a key element for better building energy efficiency. However, adding insulation, especially in retrofit projects, tends to cause pronounced thermal gradients between outside and inside, resulting in condensation build-up that causes damage to the structure and its systems, as well as incubating  mold in buildings and ultimately contributing to afflictions like “Sick Building Syndrome”.  Recognizing the critical importance of this developing industry, researchers at Fraunhofer's Institute for Building Physics (IBP) internally developed a humidity- dependent barrier layer to protect walls against moisture.

Permeability on Demand

In contrast to existing barrier sheets, this new vapor layer adapts its permeability to the humidity of the surrounding air. In the winter the membrane has low permeability, preventing water vapor from condensing inside the wall while diffusing moisture from the inside to the outside. In contrast, in the summer the sheet has a high permeability to encourage the building envelope to dry out.

WUFI, a seminal building energy efficiency modeling program developed by Fraunhofer, calculated the properties required for an optimized vapor barrier. Scientists then compared these ideal properties with those of products already commercially available. “We found there was already a plastic film used in the food service industry that demonstrated most of the characteristics we were looking for”, said Dr Hartwig Künzel of Fraunhofer IBP. “This was an excellent starting point from which our researchers were able to develop the material further into the optimized material we were looking for.”

A Force in the Market

This innovative product has made rapid inroads into the market in just a few years. In the more developed European building markets Difunorm Vario, as the product is known, has already taken a respectable 15% share of a typically fragmented market. In the United States, where the product is sold as MemBrain, the material is a top seller for CertainTeed, the rapidly-growing building materials arm of St. Gobain. Patents are pending in 36 other countries.