G'day Tess,

No, this doesn't have a zipper, it's a big rectangle, so it can't be opened up and used as a flat sheet.

G'day Ash,

Yeah, absolutely - you'll have loads of room.
The liner is 92cm wide, and the etherlight womens mat is 55cm wide.

G'day Kathleen,

The Sea to Summit Cotton Liner Rectangular is 185cm long by 92cm wide. Sea to Summit recommends a maximum user height of 185cm, which is just over 6 foot so it'd likely be a tiny bit short, unfortunately. 

G'day Ning,

I've just given this a try for you and it looks like the Sea to Summit 100% Cotton Travel Liner does fit over the Sea to Summit Comfort DLX SI RW like a sheet. The only small catch is that it's about 5cm short at one end, so maybe put your pillow up that end. 

G'day Ning,

The Sea to Summit 100% Cotton Travel Liner is designed to be an extra layer inside your sleeping bag. It'll help keep your sleeping bag clean and will stop a lot of your sweat from getting into the bag. On a warmer night, you can even use the liner without a sleeping bag to offer a mild amount of warmth.