Hey man, the blue stuff is a self adhesive sports wrap used for taping wrists/elbows etc and can be found at any chemist or sports store for about $10 per roll, the rolls are shown in the thread titled 'great pe wrap for various applications' in the wrapping forums.
A bit of additional info, check out JakeM82 and his threads on using silicone tubing instead of cloth wraps with the extender. I use this method now and haven't looked back since! The silicone is soft and squishy for good padding but it is also grippy and the strap holds very well against it so no slippage and you don't have to strap down as tight to secure it. I've managed to go for as long as 5 hours without taking it off with no negative side effects 👍
A bit of additional info, check out JakeM82 and his threads on using silicone tubing instead of cloth wraps with the extender. I use this method now and haven't looked back since! The silicone is soft and squishy for good padding but it is also grippy and the strap holds very well against it so no slippage and you don't have to strap down as tight to secure it. I've managed to go for as long as 5 hours without taking it off with no negative side effects 👍