Substrate thickness

How much substrate is appropriate? I am currently using astro turf, one layer, and it is barely a 1/4 inch thick. I'm just paranoid about burns from the UTH ...

when using a UTH you want t keep the substrate layer 1/2" thick or LESS

Substrates are NOT the right way to regulate the temperature of a UTH... a thermostat is the only safe way to do so.

If you have a thermostat set it to a safe temperature that provides a 88-92 degree basking spot without making the bottom of the cage get hotter than 95 degrees. anything hotter will cause issues.
You should also have a probed thermometer that is telling you exactly how hot the surface temperature of the substrate is that way you know how hot the cage is.

Many people use single sheets of paper towels/butchers paper/newspaper so a 1/4" of astroturf is more than enough