With our recent experiences with the costuming and cosplay communities, we've learned a lot about new materials that cosplayers use for making masks, props and armour. That added a few new words to our vocabulary and awesome new items to our inventory.
First, Fosshape. It is a felt-like polyester fabric that can be stretched and formed over a mold with heat (ideally a steamer). It collapses in thickness and sticks well to itself, forming a firm but pliable surface. It comes in two thicknesses, 300 and 600 which is double the weight. Easy to cut and paint, does not fray.
Fosshape 600 is a heavier, thicker and denser version of the 300, better for more rigorous and structurally intensive pieces of work. Takes dye quite well, mildew resistant.
Wonderflex is another heat-activated material that has a texture of 1mm thick lightweight plastic rather than fabric. It is pliable and sticks to itself while heated and becomes tough but flexible after cooling down. It is very popular in making prop armour and other rigid costume pieces.
Here are some samples of what Fosshape is capable of. It cuts well with scissors and Xacto knife, and can be formed around various objects and hold that form after cooling down.
It can be painted and formed into relatively simple...
... or quite complex shapes: