WonderFlex and Fosshape

Wonderflex is a malleable composite - like a thick plastic sheet - that you can cut and shape with heat from a steam iron or heat gun. it sticks to itself, so you can build out large costumes, or do intricate piecework to build masks and stages. It is like buckram but easier to use and flatter-more consistant surface for making body armor and helmets and such.

Fosshape is like a heat malleable felt that you can cut and pull and shape for hats, masks, giant but lightweight costumes and props.  Steam iron works best.  Milliners love this for awesome shaping - easier to use than buckram and lighter weight, so your fascinators float.  It can meld to itself with heat, or you can glue, staple and sew it.