As I've accumulated the clothes for next year's through-hike, I've noticed that most of them are labeled "machine wash cold, delicate cycle; tumble dry low heat". But I've heard hikers claim that they'll wash on the most vigorous cycle because of the extreme dirtiness, and dry on high to cut the time.

I don't know if a delicate cycle is adequate, not having the stomach to accumulate a load of really filthy clothes if I don't have to. And I don't want to risk brand new polyester and wool clothes on a high heat experiment. (I remember old polypropylene base layers would melt at high heat.)

What's the reality? Are laundry instructions needlessly cautionary, or are through-hikers destroying their clothes in the wash?