My gambeson is a Matuls aketon, made similarly to fourteenth-century ones out of many layers of raw linen quilted together. It looks a lot like this image (only grimier). I put it in the washing machine with a couple of towels to keep the load from unbalancing. When I pulled it out, it weighed--I'm not exaggerating--forty pounds. The spin cycle on the machine did nothing to get the water out.
I took it to the sink at the laundromat and squeezed about two liters of water out of it. Then I lugged it home, put it in the bathtub and trod on it for awhile. After that I hung it over the rail of my balcony and I've been squeezing a cup or two of water out of it every few hours all day. Matt2 says that when he washed his kit, it took a week to dry.
I can't imagine fighting in that thing in a downpour. It would eventually weigh more than steel armour. The battle of Agincourt must have sucked.