I've just found something interesting - well interesting to those who sew or do other crafts which involve a self-heal mat ...

The first question to answer is 'what is a self-heal mat? with 'what are they made of?' and 'what do they do?' following closely behind.

A cutting mat is a measurement tool used for sewing and crafts projects. Generally a cutting mat is a rectangular piece of durable material, such as vinyl or rubber.

They protect the work surface from damage, and prevent your knife blade from dulling quickly.  Cutting blades create tiny scratches in the mat surface that reclose afterward; thus the description "self-healing."

They don't "heal" exactly. The cuts are still there. The mats are made out of a rubber that expands slightly when cut, which pushes the two sides of the cut closer together so you still have a mostly smooth surface. 

They expand because the inside is compressed (under pressure) and the film/surface material is holding them in that way so when they're damaged, they get released a tiny bit but are still mostly held in place by the rest of the mat. 

How to clean your self-heal mat:

• Soak in a bath or large container (to lay as flat as possible) and soak it for 15-20 minutes in a solution of 1/4 cup white vinegar to every gallon of cool water. Let me repeat, cool water. Do this every so often to help extend its useful life. 
• Then use a squirt of mild dishwashing liquid and clean the mat with a very soft brush .  The purpose of this gentle scouring is to remove the fibres that get trapped in the cuts marks preventing the cuts from coming together. 

also see:
http://makezine.com/2010/11/23/what-are-self-healing-cutting-mats/ 
http://www.core77.com/posts/17891/a-materials-mystery-what-the-heck-are-self-healing-cutting-mats-made-from-and-a-possible-alternative-17891