It's called repti-carpet and I love it. When you buy it, you get 2 pieces in the package, so that when one is soiled, you have a replacement ready.
I just pop mine in the washing machine with very little soap, and I run it through a second final rinse to be sure there is no soap residue that might irritate my snakes' skin.
If you buy some, it comes in standard aguarium sizes, but when you first use it, it'll be a little bit oversized. DON'T CUT IT DOWN. It'll shrink a little at the 1st washing and will be just right after that.
Many pet stores carry it, or you can order from someone like LLL or another big dealer.
Hope that helps.
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2.1.0 Kidletts
0.0.1 Ball Pyhton (Rex)
0.0.1 Okeetee Corn (Maizey)
0.1.0 BCI (Ruby)
0.1.0 Cat (Ginger)
1.0.0 Pughuahua (Ranger)