Some general information on foam rubber I found when researching mattresses.
Latex: (natural rubber)
Polymer: Plastic: Polystyrene, Polyethelene, PVC Rubber: CR (chloroprene rubber, neoprene); SBR (styrene butadiene rubber); NBR (acrylonitrile butadiene rubber); and EPDM (ethylene propylene diene methylene)
Open-cell sponge rubber - air or gas can pass through them similar to the way water is absorbed by a dish sponge.

Closed Cell sponge (expanded rubber) Floats, Functions well as a shock absorbing material.

Products — Bergad Specialty Foams & Composites offers,
Viscoelastic Foams
High Resilience Foams
Injection Molded Viscoelastic Foams
Containment Berm Foam

last updated 16 Mar 2006