Retaining heat questions

[Cmwells90]

So I'm using an Exo Terra Large Heat Wave Heat Pad to heat the enclosure for my BCC. I'm having no problems getting the heat in her warm hide (I'm also using a thermometer and a thermostat). But I would like to increase the ambient temperature, it seems that the heating pad is really only heating the substrate directly above it, and not the rest of the cage. Any advice to increase the general temp of the cage? I am using a glass 20 gal tank, and I know most of the issue is because the tank is glass. Anyone know of an insulator that would help retain the heat? I've seen online about using a polystyrene base under the heating pad, but I don't want the glass to crack if it gets too hot, or the Polystyrene to melt (Not sure what it's melting temp is.) plus it seems like the larger issue is the glass walls, so maybe some insulation for the walls? Also the lid is mesh, but has been covered with plastic to increase the humidity (which worked great), with a few holes provided for air.

Any ideas would be great, other than using a different cage, I like the glass for the aesthetics.