Bikram yoga mat question

I was at a Bikram studio today in Cambridge, MA and they have old mats that I was very impressed with. They no longer sell them, however. I was told they are made by Prana. They appear to be like a very think felt/rubber mix and they fold. I looked online to see about buying one, but the mats that I see don’t appear to be like the ones I saw. Does anyone know the mats I am talking about? Thanks