My sweater gloves are rough, but they will work. I followed the Gunny Sack's directions, and it was a quick and painless project.
To start, I just cut off the sleeves of an old sweater. This one wasn't 100% wool, or else I could have felted it, which is recommended for any resweatering craft. Felting a sweater will shrink the sweater and help the material's threads stay together better.
Just have to try on the sleeves to see where a small cut needs to be made, for the thumb.
Sew around the thumbs, zig zag (and with color-coordinating thread, not bright white like mine). And then, sew down the sleeve curving in to make the mittens tighter on your arm. Then, sew around the ends to keep the material from unraveling and then you'll have your own sweater mittens!