To me, the most exciting part of crocheting a stuffed animal is using stuffing! One of the most common types of stuffing is polyester and is soft and easy to use!
The trick to even stuffing is to pull it apart into smaller clumps and place them in your object one at a time. While a bit time consuming, it creates a rounder and smoother look and is worth the effort. Continue placing in one clump at a time until you are happy with the fluffiness of it and simply close up your piece!

