When you arrive in a YHA1 youth hostel bedroom, you will see bunkbeds. On each bed will be a mattress with a bottom sheet, a covered pillow and duvet (in a neatly folded pile) and what looks like another sheet. It will not be another sheet. It will be an example of the infamous 'sheet sleeping bag'.
What's a Sheet Sleeping Bag?
The sheet sleeping bag is a sheet slightly more than twice the length of the bed. It is folded over, and the sides are sewn together for a length of about two feet from the fold. The top of the sheet is asymmetrical. One layer is a single layer of sheeting, the other has a open-sided pocket sewn into it.
This produces a rudimentary sleeping bag: the pillow goes in the pocket, the duvet goes on top, the sheeting is folded back over the duvet, and you go in between the layers, theoretically not touching any of the bedding except the bag.
What's it For?
The sheet sleeping bag has a very practical purpose. It is there to protect the bedding from contact with the guests. Don't take this as a slur: without the sleeping bag, hygiene would require that the bedding be changed every day. If the bedding is instead washed at reasonable intervals, and the sleeping bag changed every time a different guest is to use the bed, the laundry is much more manageable.
Making the Bed
To make the bed, first remove the duvet and pillow from it. It's much easier to start with an unobstructed mattress.
Unfold the sheet sleeping bag and find the pillow bit. It goes at the end of the bed where you want your head to be at, on the bottom layer. Pull the rest of the sleeping bag straight, but don't tuck the edges in if you want any wriggle-room. Lay the duvet on top. Fold the spare part of the top layer (it will reach over the pillow) back so that it covers the top part of the duvet.
YHA hostels also provide blankets for extra warmth. They may be in your room or on the landing somewhere. They are warm but scratchy2, so put them on top of the duvet and underneath the folded-back part of the sheet, to protect your chin3.
But it's Not Long Enough
If you are longer than standard single beds are designed for, then you are likely to be cramped in the sleeping bag. The easiest way to deal with this problem is to just live with it. If you are likely to go hostelling a lot, you can buy or make4 yourself a longer sheet sleeping bag, and you might want to consider a lightweight, compact sleeping bag in place of the duvet provided - although you will still have to put it inside the sheet sleeping bag to keep the blankets and bottom sheet clean. If you can, sleep on the bottom bunk. The top bunks have wooden boards around them to prevent dangerous falls; the bottom bunks do not, so your feet can overhang the end of the mattress. Rucksacks can be placed at the end of the bed to extend the length of the mattress.
When you went to sleep, your sheet sleeping bag was neatly placed between you and the world. When you wake up, it may be rucked to the side, twisted around you, or in a small crumpled heap at the foot of your bed anchored only by your head on the pillow. It depends how much you wriggle.
If you are leaving the hostel that morning, remove your sheet sleeping bag from the bed and place it in the linen basket on the landing. It's generally considered polite to fold your duvet and replace it and the pillow on the bed, as you found them. If you used a blanket, return that to its place as well.
If you are staying another night, you'll want to remake your bed neatly, because you will be sleeping in it again.