After cutting up the EZ Snap shade material for my RV windows, I had a little bit leftover. So, I used a small rectangle of it with 6 snaps to cover my shower skylight.
It makes a huge difference in the amount of heat that can come through but still lets in a reasonable amount of light. It also should help protect the plastic skylight material from UV.
I had to be careful when applying the snaps to the skylight not to crack the thin plastic.