Try this, Grab a match and a piece of heat shrink tubing and see if the tubing will burn. I tried some plain clear tubing about 3/16 inch diameter and some of those heat-shrink-with-a-ring-of-solder-in-the-middle things. Both caught fire pretty easily--I mean actually in flames.
Maybe I am buying the wrong stuff. But this seems all wrong to me. This stuff covers electrical joints and joints are where things often heat up.
Let me know how your stuff tests out.