This is the ResMed Slimline Tubing for the the AirSense 10, AirCurve 10, and S9 Series CPAP machines.

The 15mm, small diameter air tube is ultra-light, flexible and provides a unique alternative to bulky, generic 6 foot hoses. ResMed's SlimLine Tubing is lighter and many times more flexible than standard tubing. It works well with smaller lightweight masks, as it is less likely to pull on the mask and break the cushion seal.