Addtional advice: After handwashing, roll the undies in a microfiber towel (we bought ours from Rick Steves online) - this will absorb more of the moisture and things will dry more quickly.

We also bought undies from Tilley's online - perfect for travel, fast drying. Took only 2 pr each for our trip to Europe and with above method, worked out great.

Ok now I know this post is old ;-) but to Cira's originally proposed problem it's a lot easier to 'pack light' by eliminating a single extra pair of pants or a couple shirts and take whatever clean underwear you need for the trip.

Sure a different strategy is needed for long-term travel, but this trip was only for 6 days!

Pack 3 pairs wash 1 pair a night, even if they take longer than overnight to dry, you'll always have undies.

I just had to add my Irish experience. I went for 2 weeks (end of Aug/beginning of Sept) and we moved just about every night. So about halfway through, I decided to wash some socks and undies. Unfortunately, I didn't consider that it was IRELAND and rainy for part of almost every day. They didn't dry for 4 days, even being discreetly laid out on the backseat of the rental car all day long for 2 days! LOL! So I was very interested in how to dry undies, even though I will never travel without enough in the future.

Pack your oldest, rattiest, most holey underwear. Wear them and throw them away. No washing and by the end of your trip you have extra room in your suitcase for souveniers. My sister and I always do this when we travel together. We keep a stash of ratty underwear just to take on trips.

Buy the fast-drying underwear. Do not take cotton.

If the climate is hot and humid, the cotton will never dry, and it will get stinky.

I never travel with cotton underclothes. I bring synthetics (Tilleys, TravelSmith, Magellan's all sell them) and get one of those twisted tubing clotheslines (Magellan's). Wash in the sink at night, roll in a towel, hang in the clothesline, you will have dry underclothes by morning, guaranteed. You will really only need 3-4 sets, at most.

Can't you just flip them over ??

When we were in Hawaii, we stayed in a place that had no AC but had a fan. I washed all my underwear and dangled it over the fan to dry and then we went to breakfast. When we got back, they had cleaned the room early. I'm sure they thought I was a nut with all my undies blowing around. I usually rinse and hang them on the shower rod, or if it's humid, I'll use the blow dryer.

Hang them on your fanny pack and take a walk over to Bellagio to watch the fountain show. By the time the show is over, your panties will be dry. Then just stuff them into the fanny pack.

Go Commando.

I found a company that sells inexpensive cotton underwear they are marketed as disposable but you can wash them a couple times by hand
than through them out. I am very picky about my underwear but was so pleased with this company wearbriefly. I thought the name was kinda cool too. I tried these after I tried a pack of onederwear
and the sizes were super small. I got a pack of boxers for my boyfriend and he did not fit in the XL ( he is only 170lbs about 5' 10"). Anyway check them out they are great. I think the website is www.wearbriefly.com.

all underwear is disposable