I am sure some of you are shaking your heads & saying "yep... Kris has finally lost it!", but I made wool underwear! I wanted these mostly for running, since you need your underwear to be made of a moisture wicking material, but they can be worn any time.
You'll want to use lightly felted merino wool for these... felted enough that the edges don't unravel when cut, but is still stretchy & drapey. For your pattern, use a pair of underwear that fit you well, but need to go (I won't be showing you the underwear that I used!)! Take your old pair of underwear & cut off the waist band, then down the center. These pieces will be your pattern.

Take your pattern and cut out 2 pieces, making sure to add 1/2" on each side, for seam allowance, and because your regular underwear material will most likey be slightly stretchier than the wool is. You should end up with 2 pieces that look like this:

Now sew the ends together, wrong sides out.
Now turn it, so the seams are down the center & sew the bottom pieces (the crotch) together.
Now to make the waist band, cut 2 piece of wool that are a little shorter than the underwear (you may want to measure your waist & take it down a couple of inches to account for the stretch). Your waistband will end up being less half the width of your pieces, so make sure they are wide enough. In hindsight, I could have used a little more waistband on mine, but they are fine as is too.
Sew the ends of your pieces together, wrong sides out.
Now you will take this & fold the width in half, seams in, right side out & sew this to the waist of your underwear. Your underwear should have seams out still, and you will be sewing the waist band to the inside of the underwear. Since the waistband is a little smaller, you will need to be stretching it as you go. When you are done, and flip them right side out, they should look like this:
Now flip them back wrong side out, and repeat the waist band process on the legs (only smaller, obviously). When you are done with that, they will look like they are done, but you have one more step, adding a panel to cover the crotch seams.
Just cut a small piece to the shape of the crotch, and sew it to the seams on either side.
Now you are done!
I took mine for a test run last night (went jogging in them). The only con to wearing these that I found, is that they are slightly more bulky at the seams than regular underwear, so where they are fine under jeans, I had definite panty lines under my tighter fitting jogging pants. I think i'll work up a pattern for a more "boy short" style, using the original seams, and that should eliminate than problem. The pros? There is no sweat smell on my wool underwear (or even on the synthetic jogging pants I wore over them), that is usually on my clothes after I run (I can't believe I am telling you all this!), there was no unpleasant dampness from sweat while I ran, I was the perfect temp (neither hot or cold) in that region while I ran, and they are really cute looking! Of course these can be worn for everyday underwear too. I would imagine these would be fantastic for any mom that has to sit in cold bleachers!