I wouldn't sweat it as long as speakers are elevated...I'm sure others are going to mention Italian marble, spikes made from rhino horn, and 6ft bamboo stilts... Don't bite
The best material for a platform for floorstander
.......I have a concrete floor with Berber carpeting ...not too thick with pad maybe 1/2'' total.... In an effort to get them off of the floor as it is a basement, the room is temperature controlled ... the spikes on the speaker do raise them about 1/2 '' to 3/4'' from the carpeting and the spikes I am pretty sure are anchored on the concrete......just to get them as I said ; '' off of the floor '' - any ideas ?