Self Amalgamating Tape, is a stretchy rubber tape, that is used for a number of purposes.
Wireless engineers use self amalgamating tape to seal around coaxial cable connections.
By wrapping self amalgamating tape around where the cable goes into the connector, keeps moisture out.
The tape is made from stretchy rubber, and is not sticky.
To use the tape, you peel the plastic backing off a short piece of the tape, and stretch the tape, as you wrap it around the coaxial cable.