This is a post by a lady called Paige Russell She has explained the best way to felt a jumper.
1. The fiber type / blend:
I have found that a blend of 65% or higher wool content yields the best results. 100% wool is desirable, but not necessary.
2. The knit stitch:
This one is a little harder to pin point or predict. I’ve found that certain knits refuse to felt no matter what I do – even if the wool content is high. The best thing to be on the lookout for is stretchiness. If a knit is too stretchy, it will most likely not felt well. But I say if in doubt, try it!! If it’s something that’s just been taking up valuable closet real estate, you have nothing to lose!
Step 2: Get Felting!
1. Place sweaters in a washing machine and chose a long, HOT cycle.
*For extra agitation, you can add a pair of old running shoes to the cycle. These will help ‘pummel’ the fibers into felted submission.
2. Add half the normal amount of washing detergent for a single load and start the cycle.
3. Once the wash cycle is complete, transfer the sweaters to the dryer (not the sneakers, if you chose to add them to the wash cycle).
4. Chose a setting that is long and HOT. ‘Cottons’ is usually a good one to use.
When the dryer is finished, pull the sweaters out and give them a good close once over. If the fibers do not appear bound/matted enough to not fray when cut, you can repeat the above wash/dry process as many times as needed. For your reference, the three sweaters pictured took 3 rounds of washing and drying to achieve their felted state.