I feel it is important to differentiate between the various BeamFilters...
The FMx3 IR BeamFilters use glass.
The F04 and FMx4 BeamDiffusers (aka BeamShapers) use a highly specialised (and expensive) LSD® Light Shaping Diffuser featuring holographically recorded, randomized surface relief stuctures that enable High Transmission Efficiency (up to 92%), and Controlled Angular Distribution, while providing high quality Homogenised Light. The material is a 'shatter-proof' polycarbonate.
The FM Series FMx5 (red) and FMx6 (blue) BeamFilters are AR multi-coated tempered glass to maximise transmission efficiency. These coats can be scratched and it is best to be careful when cleaning them.
The F05 & F06 "E-Series" red and blue BeamFilter (current version) are polycarbonate I believe.
The FMx7 BeamCovers are HA aluminium alloy.