Bowlus Maxi Gap Seal Tape is made by Michael Bowlus. It has a great reputation as a fantastic gap seal tape. It is polyethylene tape. It is extremely stretchy which allows it to follow the complex curves around the leading edge of the wing root although no tape can form to every curve. This tape utilizes UV protection so that is lasts longer in the sun than other products. That is very important for gliders that remain assembled for long periods of time - especially if they sit in the sun all the time. The tape is designed to stay in place and not split even when you take off from an airport with high temperatures, fly at high altitude in low temperature environments and land back in high temperatures. Bowlus tape is a brighter white.
Bowlus Maxi Gap Seal Tape is better than the 3M polyethylene tape, and much less expensive.
AMS Flight is the Europe distributor for Bowlus tapes.