Thanks for this! Yes, it seems the santhata was made of fabric that is similar to felt. I will add this to my discussion of the term.
When considering the appropriate translation, however, the main issue at that the term santhata is specified mostly by its usage, not by the kind of fabric it is, that is, the santhata was a specific kind of large cloth used as an underlay or to warm oneself, like a blanket. For this reason I think blanket is still a better rendering.
I will edit my discussion of the santhata in my Appendix of Technical Terms.