Some years ago, some school jumpers in my sister's house got a bit too small too fast, my sister sourced another school jumper with less wool content (no wool), and I said that I would make something out of the felted ones - 4 years ago..... and I finally have.
I tried out some slipper patterns, and found a very good tutorial online (link here). The first pair I used a school jumper and the sole was more jumper, 2 layers of curtain interlining, and a mock suede upholstery swatch I was also given a long time ago. The tutorial online, the maker used some wool insulation, which looked brilliant, but I haven't a clue where it could be got.
These slippers were too light! My toes were frozen, so I had to up the ante, especially a my old slippers I had been wearing were falling apart. But when I looked at the old slippers I noticed they had a plastic-y underlay type layer in them, so slippers #2 had extra linings and underlay.
Slippers #2 are super cosy, there is a layer of wool, interlining, underlay and suede and they are also wool lined. As the soles were getting a bit thick, I machine stitched an outline on the base to keep all layers in place before I sewed uppers and soles together. I blanket stitched one and machine stitched the other. The blanket stitched ones are probably more comfortable but now that I am wearing them I notice the difference less and less. The became incredibly comfortable incredibly quickly and they are now the slippers I wear.
I was explaining to my nephew Alex how I had made slippers from old jumpers on the phone. Alex (10) was very skeptical so I asked if he wanted a pair, and slippers #3 are for him - I used some of slipper#1 so I would have 2 monograms (on very obviously off), lined in the plaid from last weeks overblouse, and an extra layer of wool in the sole (so that is 2 layers wool, one underlay, one interlining, and one mock suede sole) should be super cosy.