I might think he may not wear a garment of wool over one of flax, and one of flax over one of wool; it is, therefore, written (woven) "together," but each by itself is permitted.
R. Chananiah b. Gamliel says: Whence is it derived that one may not hatchel strips of wool with strips of flax to belt his thighs even though there is a band of leather separating them? From "together." This is to say that a sack and a basket (joining wool and linen) are considered a union in respect to kilayim.
"wool & linen together": but each by itself is permitted.