Housing made of transparent plastic. Removed gas system, housing, handle, lock carrier, etc. for illustrative purposes.

The main components of the G36 are made of glass fiber reinforced plastic, with the idea to lower the weight of the firearm and lower the level of maintenance needed.

In Germany the model is called “Schnittmodell“, a cut-away model. The model pictured is also transparent, apart from the metal parts.

https://www.thefirearmblog.com/blog/2019/02/13/the-transparent-heckler-koch-g36/