When I was first testing this pattern, I made three frogs. For the first one, with the gray and blue sweater, I completely used acrylic yarn. For the second frog in the cream and gray sweater, I used cotton yarn for the sweater only and acrylic yarn for the rest. Both had a gauge of 4, so the thickness was the same, but the acrylic yarn did give a bit of a fuzzier look. For the third frog, with the maroon sweater, I used velvet polyester yarn that was a gauge 5 yarn, so that frog turned out slightly bigger than the others with a smaller gauge. Some of my testers used blanket yarn. You can use whatever yarn you prefer. You can also use whatever colors you like, both for the frog and the sweaters. This is a very customizable pattern.