I've been meaning to make these available seemingly forever now.
I use these sturdy little, lightweight, low density off cuts from making things to elevate my drop rings in the kiln.

(12) 1" vboard pieces

Stack 'em in combination with each other to have more control over your drop height. Sold in multiples of three because there's no need for four legs under your mold. :-)

Note: Thickness of just about every material I order seems to be variable these days. These pieces are the exception. Thickness seems to be consistent and reliable. They can always be easily thinned on a lap wheel or even using wet dry sandpaper on a flat plane. (I do it all the time)