29" : https://www.rei.com/product/15809…29-x-18-24

27.5" : https://www.rei.com/product/15809…75-x-18-24

Yes, there is a flow of cheaper chinese TPU inner tubes available now on Amazon/eBay/Aliexpress etc, but some people prefer the "OG".

TPU inner tubes are great if you want to save weight and rolling resistance on your bikes but you don’t want to go tubeless. They retain pressure far better than latex tubes and are a bit more puncture resistant than the regular butyl inner tubes, for a fraction of the weight. Also much smaller in size, so good option for MTBers that are tubeless already, but want a small compact spare tube to haul around "just in case" (this is why I have some, but I’ve opted for the cheaper AliExpress version).