i wash as soon as it comes through the door, well before i need it. i don't know what chemical has been used or where it's been or who handled it.
i zigzag the edges because i find the fewest loose threads that way. i dry at hottest to get the worst over with. if i see dye in the water, i go around again with synthrapol. i don't press until i need it - only flatten it when i'm ready to store it. if it's still warm , it flattens pretty well. i only press what i plan to use for that project. i never prewash batting. i want that to shrink for puckers.