Blue tape retainers

[Chuck Guzis]

I'm getting a little tired of replacing old dried-out foam blocks to 
hold down the ends of 1/2" tapes.  Worse, some of the ones I've fished 
out have utterly crumbled over the years, leaving bits of themselves 
inside the reel.

One thing that I recall is that many tape manufacturers used a blue, 
sort of "sticky silicon" tape to hold ends in place.  This stuff never 
seems to degrade.

Does anyone know what the stuff is and where one might get a roll of it?

--Chuck