It may have been rayon. I have a quilt my great grandmother made in the 1930' and 40's and one of the fabrics is rayon. By the way it is the only one of the fabrics that has fallen apart all the cotton is still going strong.
Depending on the type of quilt it is during those times you used what you had.
Here is a good article on vintage synthetic fabric it may be any one of these
forgot the link :oops:
http://www.fabrics.net/joan500.asp