The Polar T31 Strap is the only option to keep your T31 alive, specially if you use the T31 in the swimming pool.The swimming pool water, loaded with lots of chemicals not only destroys swim-suits but any elastic fiber.This strap is not the exception. I am using my third strap in 12-15 months.I believe the design is very good, and the material is as good as is possible given the stress conditions it is used in.Do I recommend it? Yes I do. Would I buy more, I sure did (I have bought about 6 (and used 2 + the one that came with the transmitter)Polar Elastic Transmitter Strap Medium (34-55 Inch Chest) for T31 or T61 Transmitter