I have always wanted one of these.  Could also use toaster oven to heat the plastic. From Sci-Spot.com Cast with...

by Pedro J. Lemos

Excellent tutorial from Sew Mod .

Pictoral Tutorial from Onel Love these bears.

This is a cereal box project for me.   Combination of a relief plate and a stencil plate.

at makedo

Yokoso from Tokyo "I hope that this blog will  inspire you   to make something out of cardboard   for yourself or your...

These cuties are generously shared by Runo. She has put a lot of work into her pictoral tutorials and patterns.

or Pom Pom maker.

I would make these from felt as an addition to the costume box.

Generously shared at No Pattern Required.