I am sure we have all used and perhaps misused shrink tube.
Does anyone know if this has really been evaluated and what is it really appropriate for?
I am guessing class 2 low voltage but I am not really sure.

It looks like at least some is rated at 600V. Click Here for more info

I'm sure that this is something that we have both used a ton of in our electronics related lives. Even good quality heat shrink can be applied badly. Plus, we can only guess which brand someone else has used. I just bought 4' lengths of 3/64", 1/16", 3/32", and 1/8" in my last MPJA order. The paper label on each length tells me it is "PermaSleeve" polyolefin and is UL & CSA certified @ 600V @ 125 C. But there isn't a single marking anywhere along it's length to clue you in. I often use it in conjunction with clear teflon tubing which I believe has superior dielectric properties.

As an aside, I was recently asked to order some more of the yellow silicone jacketed cable that was used for signal analysis long before I showed up. Imagine my thoughts when I learned that the 1000V rated silicone jacket surrounded a 300V rated pair. OOPS!!!
Joe

I have probably used a mile or two of shrink. Some has come in engineered "bills of material" in carefully wrapped "kits" and other was ordered from "Hos/digi/all/new/Jam" or "Bob's" electronics. None of them had a listing mark.
I do understand you never shrink a "wild hair" or pointy solder joint but I still wonder what a clean joint shrinked 30-40% is worth. Bear in mind the thickness of the finished insulation depends on the anount of tube you started with. A "close fit" is probably not a good thing.

Some types of heat shrink are rated up to 35kv.