I knit matching Chulo hats (Andean hats) for my son and granddaughter and puzzled over how to block them. In the past I would have steamed them with an iron but lately I do not want to bring out the iron at all. So I looked for something head shaped around the house. We have a six foot mannequin but his head seems narrower than most adult men's heads. I did not find anything comparable for my two year old granddaughter's head. So I decided to try using balloons, just cheap party balloons from Wally World. I wasn't sure about the final shape though. The results are great. The balloon swells up to fit the knitted shape of the hat. I have to admit that the hats looked like disembodied heads lying on the mat for a couple of days. They dried quickly, I was just too lazy to take out the balloons. And they fit my son and his daughter.