Perma Pure uses a proprietary epoxy with a high corrosion resistance to bundle the tunes in the “header”. This material has been tested to work well with Nafion and keeps the seal between the sample gas and the purge gas. The same material is used in the FC100 Humidifier. For larger FC humidifiers, a proprietary polyurethane is used to perform the same function. Because this product was designed for fuel cell applications where only clean water is hsed, the enhanced corrosion resistance of the epoxy was not required and a more suitable material was found that would work better with larger bundles (up to 10,000 tubes on the FC800).