Many materials can insulate glass & are easy to cut & attach: cork (the 1/4" thick kind, sold in rolls), corrugated cardboard, self-adhesive carpet-tiles, poster-
board (1/4" thick, with foam core), packing bubbles (sold on rolls- also used as the core of hot water heater "blankets"), rigid foam sheets, etc. Your choice!
I use all glass tanks & for best appearance, I like to tape on scenery first, then you don't even SEE your insulation. Most snakes appreciate having the back
& sides of a glass tank covered, & you can even cover the lower 6" across the front if you want. Don't forget the bottom! If you use UTH, it needs a bit of
space to breathe, but otherwise insulate under the tank to help the heat rise. If my tank is on a wood cabinet, I use ceramic tiles underneath the UTH as a heat
sink, & to help keep the wood from drying out from long-term exposure to heat. If the tank is on an aquarium stand (with open bottom under the tank) you can
attach some welded wire or sheet metal underneath the open area, insulate ON that & under the UTH, to help keep the heat going upwards where you want it.
Be creative & safe, that's the main things. Minimize use of anything flammable near the UTH...even though hard to burn, things do dry out in time, especially
with the higher heat used on BP cages (or other tropical species).