Wool yarn turns to felt when immersed in hot water and agitated. This can be done by hand, but is time consuming. Machine felting lets your washing machine do the work. Felting an item made from wool gives it a dense texture, smooth surface and more durability. Keep in mind, however, that wool shrinks during the felting process, so always knit or crochet the item larger than you want the felted size to be.
If your items are handcrafted, make sure all yarn ends are woven in. Place the wool items inside a lingerie bag or a pillow case and knot the end to keep the items inside. Add the bag to your washing machine with sturdy clothing, so the items have something to rub against to get the felting process going. Clothing made from denim is a good choice for this step.
Washing Machine Settings
Set the water temperature on the washing machine to hot with a cold rinse. If your model has multiple speeds, set the washing cycle for the longest time with maximum agitation. You want the wool items to get a good workout. Add a little wool-friendly washing powder to the load before you start the cycle. Fabric softener isn't necessary for the wool items--they'll be removed before fabric softener is dispensed--but you may want to add some for the other items in the washer.
Let the machine agitate for 5 to 10 minutes, then check the felting process. You may leave the wool items to agitate longer if necessary, but you don't need to wait for the machine to rinse or spin. Remove the items from the machine when they're felted to the degree you want, rinse them in cold water, then squeeze them and roll them in a towel like a Swiss roll to remove excess water.
Drying and Blocking
Reshape your items using pins on a styrofoam or cardboard surface. This is known as "blocking." Wool is very strong, so don't be afraid to really tug and stretch your item to get it to the shape you want. Once it dries, the shape is permanent unless you go through the felting process again--so it's important to get the shape right the first time. After drying, felted material can be cut and sewn to create bags, appliques or other fibre pieces.