Pure wool felts nicely and is readily available. Other animal yarns will also felt very well. i.e. alpaca
A small amount of other yarns that have been blended with the wool, will also felt, BUT the parts that are NOT predominantly Wool, will not felt. The amount of Non felting fiber determines the look and can produce a very interesting fabric.
An example of this, is the “Landscape Purse”, (a Lion Brand yarn) a picture is posted in an older part of this blog. The acrylic bits and pieces ” pop out” of the felted wool.
Wool yarn is spun from different “grades” of quality and processing. This makes the felting process behave differently from one Brand of yarn to another.
An example of this, is the yarns that have been minimally scoured at the mill. These oils need to be washed out of the yarn. The automatic washing machine and detergent does a good job of removing the oils.
I must CAUTION, please watch your work during the felting……………………….or you may end up with something you didn’t want.
Have fun, experiment. At the worst, you will have made some nice “Hot Pads” for your kitchen.