I made this GoPro lens protector so that when I go airsofting there is no risk of the lens getting cracked from a BB. The printed part is actually a frame that secures lexan/polycarbonate to a GoPro Session. The frame clips on to the GoPro Session holder.

After printing you will need to glue a 44mm x 44mm piece of lexan to sit in between. The sheet of Lexan I had was 2.5mm thick and has been thoroughly tested on youtube to withstand high impacts from airsoft guns. The glue I used to secure the lexan to this frame is made by Loc-Tite.

Cutting the lexan was done with my skill saw.

Glue: Loctite - Plastic Glue [2 part]
Lexan: 44mm x 44mm x 2.5mm thick.