The poly threads stretch and do not do well on a lot of machines... cotton is always bes and a good to to boot.
Hold up an look at it if fuzzies all over NO.
Poly thread is usuall wound to fast on most machines and stretches it then when stitched out it drays up, that is why you get bad puckerd seams....
I think the poly thread that was being talked about is the clear threads... yes they willmelt but not the cotton/poly blends, but not the best to ever sew a quilt with.
Silk thread is the best for english paper piecing first and second a fine cotton.