The internal structure of the rim forms an internal arch massively increasing stiffness which means excellent resistance to bending and a nice strong wheel. The rims need to be sealed with tape such as the 25mm Yellow spoke sealing tape to make them airtight and protect the rimstrip. You also need a flow rimstrip or Olympic valve for running them tubeless, or they can be run as normal rims with tubes.
There is a specially designed Flow rimstrip which weighs just 57g, or you can use the even lighter yellow tape / valve stem combination. We'd recommend the yellow tape if you want to use tubeless-ready tyres (UST, Bontrager, Specialized 2Bliss for example), or the rimstrip if you want to run standard tyres with a latex sealant.
Weight 26": 480g, 650b: 488g, 29er: 532g