Both systems provide some capabilities like thermal insulation or light translucency. However, ETFE foil cushions offer some benefits over glass.
ETFE is a very flexible material and is able to cope with large deformations before breakage. Elongations of 200-300% are possible. As being prestressed, it can accomodate the live loads. Glass, on the other hand, is very brittle and works as a plate. As a result, it is subjected to bending moments. ETFE is on the other hand is mainly subjected to tensile stress. The outer layer of an ETFE cushion is the most stressed layer where inner layer is the less stressed one. Middle layer takes almost no load, so basically it is used to created two compartments in the cushion.
The dimensions of a single panel is a major difference between glass and ETFE. ETFE can literally be quite long whereas glass panels are rather limited in size.
ETFE is a modified copolymer which is manufactured and processed by the same methods associated with most thermoplastic polymers.