The caps are made out of 80% sheep’s wool, and need a few touches of love and care to stay with you through the years.
The wool is provided by South American sheep, mostly Uruguayans, and is processed on the Norwegian west coast. These sheep provide softer wool than the Norwegians do.
Do not tumble dry! You may tumble dry it, but it will become something else than what it is right now. That is called felting. So don’t tumble if you want to keep it like it was when you got it.
Wash it at a 40 degrees (celcius) wool program. Unless you want to go all adventurer and hand-wash it.
A note on stretchiness: If you happen to have lent your cap to a friend with a rather large head, and as a consequence of your thoughtlessness it no longer clings to your head, then do not despair. Just dip your cap in hot water and let it dry, and the woolliness of the wool will make it shrink back to perfectly clasp your head again.