I have just read a caresheet which says that aspen is the best substrate for boas - until then I was going to keep my new acquisition (we pick her up Saturday and she is one year old) on a mixture of newspaper and paper towels with maybe some machine shredded/recycled paper thrown in.

But after reading the caresheet (RioBravo Reptiles) I'm not so sure .... but I know a lot of the breeders and keepers swear by the newspaper/.paper towel stuff.