It is a way of life for nomads in the Middle East - there they construct whole tents made from felted wool, which hold out the elements and are quick to erect or pack up when they need to move on.
This amazing process is only possible with animal hair, as these fibers are formed from protein and each fiber is covered in tiny scales. When soap, heat and water are added to the mix and the fibers are rubbed together, the scales interlock and cling to one another, shrinking and thickening the fiber wad, forming a new fabric - felt.
There is no way to reverse this process - once felted - always felted. That's why the washing instructions for wool sweaters say "Hand Wash, Dry Flat", because if you toss them in a regular wash...they felt!
Actually, there are 3 methods of felting - two wet and one dry.
The wet methods are...
The dry method is...
On the whole, it's an inexpensive craft to try - you don't need much in the way of equipment.
You can felt projects you have made already, as long as they're made of wool or other animal fiber. They say that a yarn with as low as 50% wool content will felt. A yarn with a higher percentage of wool will felt better (especially merino, as it's so fine), but you may also want to try alpaca, mohair or even dog hair blends.
Felting is very forgiving, especially if you're purposely machine washing something that you've knitted or crocheted. The stitch definition tends to disappear, so your stitches don't have to be perfectly even.
You know, I've even heard it asked..."if sheep are covered in wool, why don't they shrink when it rains?" Well - the answer is simple, it's the combination of soap, hot water and agitation which forms felt. So, technically if you popped a sheep into a washing machine, then yes - its' wool would shrink. BUT PLEASE DON'T EVER TRY THAT!
Let's hope I've whetted your appetite to give felting a try.