I tried to knit a Pussy Hat for the Women's March on Washngton, but I ended up with a mess of yarn. Never mind. I went to Goodwill and bought the pinkest sweater made from the thickest yarn they had. Then I cut it into pieces, making sure to leave as many finished edges intact as I could. There were a couple of big pieces that I could just fold over and sew up the sides. I used yarn from the sweater but I think any thread would work. Just sew enough to keep the cut sides from unraveling. To see the nice patterns for knitting or crocheting these hats, go to: https://www.pussyhatproject.com/knit/
Step 1: Cut Up a Sweater. a Scarf Would Probably Work, Too.
Before you cut, look at how the sweater is put together. Often the front is sewn to the back, sleeves are sewn to the body. Try and figure out which pieces you'll use and leave the edges of those pieces intact by cutting on the far side of the seam. If there is a finished edge, like the hem, preserve it.
Step 2: Find a Useful Section of the Sweater.
You'll need a rectangle. The knitting pattern is for a rectangle that is 11" by 17". You're supposed to knit it, fold it over, and voila!, a hat. But now you just have to find a section of sweater with at least one edge that won't unravel. You can fold it sideways or top to bottom but remember the final shape will be around 11" across and 8.5" high.
Step 3: Fold and Sew.
Fold the cut piece so the good sides are facing each other (see below). Sew the open sides, leaving the opening for your head, obviously, and you're done. The stitches don't have to be super neat, but they should be pretty tight and close together to keep the yarn from coming loose. When you put on the hat, the corners become the ears. For baby hats, see if the cuffs might be big enough to go around baby's head. Then you just cut to length, turn inside out, sew across the top. Turn it right side out and you're done!
IMPORTANT: The sewing has to end up on the inside of the hat. So you have to start with the pieces you're using inside out, or make sure the good sides are facing each other while you are sewing. Hold the edges together before you start sewing and make sure it will turn out the way you want it to.