To reinforce the sole of your Felf, you can knit and sew on a second sole before felting your Felf. The concept is inspired by Bev Galeskas’s Felted Clogs, from Fiber Trends.

This pattern is an addendum to Cat Bordhi’s The Art of Felfs, designed to allow those who are tough on their footwear to add an extra layer of fabric to the slippers they make using The Art of Felfs. The pattern is posted on Ravelry with permission of Cat Bordhi:

You are welcome to post the pattern so long as it does not include my book or pattern, but a link to it, which seems to be what you are indicating. And thank you for working to improve Felfs!

Some directions are written assuming you have access to The Art of Felfs.