Step 1: Wash and dry the sweatshirt and socks. I ordered a medium and it did shrink a little, so definitely size up.
Step 2: Scrunch the clean sweatshirt into a pyrex baking dish. The more folds and creases, the better the effect. I added three pairs of socks to the sweatshirt dish and then used a smaller pyrex for the remaining socks to create a different color batch.