Tension bed sheet/blanket correctly

Question:

How can the permanent crumpling of the bed sheet be permanently prevented?

Answer:

By correctly stretching the bed sheet. Of course you could buy a fitted sheet, also called a fitted sheet. This has an elastic band sewn into the edge or is even woven entirely from flexible material. They are quite good, but they also have a few disadvantages:

As a rule, those made of flexible material are thicker, rougher and warmer. That may be good in winter, but those who live in a warm region, find rough surfaces on their feet annoying or want to feel some cooling in summer will not be able to avoid a thin cotton sheet (I personally find Tencel sheets quite comfortable).
Practically all fitted sheets become inflexible over time after all the washing. They slowly mutate into a "normal" sheet that begins to crumple. Especially the edges are endangered.
Fitted sheets are often boringly uni-coloured.

Maybe you also have sheets that have the same pattern as your pillowcases, or you just love the pattern. New pillowcases are often only available as a set and not quite cheap. In all these cases it is not an option to buy a new one. But no problem, in the following I will show you how you can stretch any crumpled bed sheet permanently with little money and without having to leave your home.

What you need:

8 bed sheet tensioners made of metal. For example, you can find them by searching at finddealsfor.me and have them delivered directly to your home free of charge. They are called "Bed Sheet Clip Elastic Grippers". However, only use those with a metal head, even if they are more expensive. Those made of plastic are not recommended, they simply can't withstand too little pull (my first attempt with these went completely wrong). The price is about 8 CHF/EUR/USD for all together.
About 6 meters of string of any kind.

Attach 4 tensioners to the edge of the sheet, 4 on each side, evenly distributed. The result we aim for is the following:

Now we have to overcome the gap in the middle with string. Just cut the string accordingly and make a knot at each end. Clip this knot inside the metal head:

Already finished.

For the sake of completeness, here are the plastic clips that don't work well:

They were fiddly and totally overwhelmed with this kind of tension. The left part with the button is made of rubber-like plastic. It is clear that, depending on the thickness of the cloth, it holds better or worse and cannot withstand greater tension. Avoid such products.