What is "upilex"

Upilex is a heat resistant polyimide film formed from biphenyl tetracarboxylic dianhydride ( BPDA) monomers. Its properties include dimensional stability, low water absorption and high chemical resistance.High Temperature Dielectric Properties of Apical, Kapton, Peek Upilex

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19920019432_1992019432.pdf It was developed by UBE Industries.

Upilex-S, along with other polyimides Kapton HN and Kapton E, have been investigated by NASA with respect to their radiation durability for possible use in the Next Generation Space Telescope, where polymer film layer sunshields must operate at low temperatures and in the presence of cosmic rays.