The only fabrics that I could actually see "shrink" before my very eyes was cheap cotton that you could actually see the warp and weft... AND a blend which I didn't think was a blend until I "smelled" it while ironing it in a finished block; the heat from the iron shrunk it!
I now wash all fabric in warm to hot water (for shrinkage &/or removing dyestuffs) and don't worry later on. A pound of prevention....