I used a fleece blanket I found on the street. An airline blanket would work fine, or any fleece garment that doesn't fit you.
There are a few tricks to this project:
Make a paper pattern so you can refer to the pattern and evolve your next pairs of socks to perfection.
Fleece stretches more in one direction than the other. Put the stretchy direction around your foot.
Stretch the cloth while doing zigzag sewing - then the seams will stretch with the cloth later.
Sew the zigzag seam so the needle overshoots the edge. That binds the edge.
If your thread tension is low you can pull the seam around so it looks whipstitched butt-to-butt and lies flat.
Step 1: Stretch Test
This particular blanket stretches most in the direction of the stripes.
So I'll make my socks with the stripes around the legs.
Step 2: Make Paper Patterns
There's a sole, a back, and a "vamp" which is the long part that covers the instep of the foot.
The size of the cloth pieces will just match the diameter of each part of the foot they cover.
No seam allowance is necessary.
Step 3: Mark the Cloth
Use a sharpie marker or anything else.
Permanent is okay, the lines won't be visible on the finished socks.
Step 4: Cut Out the Pieces
The fleece sticks together nicely, so if you're confident you can cut out two or more layers at once.
Step 5: Sew the Heel Seam
Set your sewing machine on the widest zigzag stitch it makes.
Thread tension can be low, stitch length long.
The type of thread doesn't matter.
Sew along the edge of the cloth so the needle straddles the edge of the cloth on every zag.
That will bind the edge of the seam.
Pull on the cloth as shown to stretch it. That will make a seam that also stretches when it is done.
Step 6: Sew the Side Seam
Sew them together the same way you did the heel seam.
You don't need to hem the top of the sock, it won't unravel.
Hem the top of the sock if you want, or trim it with whatever exotic furs you have handy.
Enjoy your cozy new socks!
Make a whole lot of them and invite your friends to go winter camping!