If you've ever stayed in a UK Youth Hostel you'll be familiar with sleep liners.
They're basically a thin cotton sleeping bag with a large pocket at the top to take a pillow and are designed to provide a convenient replacement to sheets and a pillow case.
Although some refuges supply cotton or paper sleeping liners most do not.
For your own comfort and hygiene we'd advise you to take a liner of your own.
The best material for a liner is silk. Silk is cool when it's hot, warm when it's cold and feels exceptionally comfortable against the skin. It's also light and folds up compactly.
We bought our silk liners new for £10 each including delivery from Vietnam via Ebay. In UK shops they'd normally cost about £30 each with cotton liners costing about £20 each.