This one's an oldie but a goodie. Refashion a knit shirt by inserting panels of fabric on the sides. The practical reasons behind doing this refashion could be:
1. make a small shirt bigger
2. make a big shirt smaller
3. get rid of unsightly evidence of perspiration
4. use tapered fabric inserts to make the bottom part of the shirt bigger to compensate for baby bump (either before or after baby)
but the number one reason in my book:
1. it's way cute.
You will need a knit cotton shirt and some fabric to make the panels. I used woven, but you could also use another knit.
Cut up the side seam from the shirt hem to the sleeve hem - right through the underarm.
Cut two panels from your fabric. If you're making the shirt bigger, just cut up the side seam and insert panels as wide as you need. If you're making the shirt smaller, remove equal amounts of fabric from each side of the side seam and then make panels that are smaller than the amount you removed. Just remember that you're replacing it with a non-stretch fabric, so that will help make the shirt smaller in itself.
You can make the fabric insert run all the way between each hem, but I also cut out a smaller square piece and attached it to the longer piece. That way you have a seam in the panel right where you have the underarm seam in the knit shirt. I think it helps the woven to bend with your arm, but it isn't necessary.
Now sew the panel to both sides of the shirt, right sides together, and hem the woven at each end. This is what the panel will look like inserted into your shirt. Now do that again for the other side.
Simple, cute, and most importantly: done in about 20 minutes! (or, 6 hours if you have toddlers)