I know there have been many posts on this forum for people looking for a super stretchy plastic and trying to figure ways to modify the plastic to make it stretchy. Well I was one of these guys looking for the same product. I have came very close to finding a product like so. The material is a two part liquid combination ( I think silicone ) that you mix part A and part B together. It's called ecoflex 00-30, it stretches like a rubber band! I tried this product and it works well but not fast by any means! It takes several hours to cure. Just my two scents.....
Product Info:
Ecoflex® Rubbers are platinum-catalyzed silicones that are versatile and easy to use. Ecoflex® Rubbers are mixed 1A:1B by weight or volume and cure at room temperature with negligible shrinkage. Rubber also cures without a "tacky" surface. Low viscosity ensures easy mixing and de-airing, or you can choose to mix and dispense using our convenient dispensing cartridges.
Cured rubber is very soft, very strong and very "stretchy", stretching many times its original size without tearing and will rebound to its original form without distortion. Ecoflex® Rubbers are water white translucent and can be color pigmented with Silc-Pig® pigments for creating a variety of color effects.