Sounds like Chloroprene rubber tubing (non-shrinkable). What color? Black is the norm. What I/D?
This material looks like a natural rubber band (an "elastic" as we say) with a wrinkled sort of finish.
Take a look at terminal on an original wire harness. The terminals are covered with black thin wall rubber (not shrink tubing as used by some vendors). Those covers are put on with a special pliers. That material is supplied by HellermannTyton see http://www3.catoya.com/asp/_1479/flash/gesamtPdf.pdf
and the pliers are at the bottom of that PDF.