50 -50 seems to work for my babies - i never noticed any problems with that.

Cotton is nice but some of it is so expensive. I buy blends and acrylics sometimes and cotton sometimes.

Hey babies wear plastic diapers and rubber pants - what's with that?

I also like to use only 100% cotton.  I prefer that for myself as well.  But I don't think there are any real problems with using other fabrics.  I find though, that it is pretty easy to get stuff that is 100% cotton so if that is what you want for your baby you should have an easy time avoiding other materials.