The door I used was a bit longer than 2 feet. It coincidentally worked out to 2
You want to create a really long continuous tube of sock material.
You will want to create a pair of tubes connected lengthwise so you can slip it under the door. The foam pipe insulation pieces will fill out the sock tubes and hug the bottom of the door.
To extend one sock:
Cut off the end of the next sock.
Flip this sock inside out.
Insert the first sock inside and align the top edges.
Sew a seam around it to join the socks. Be sure to stretch the seam as you go along so that the sock can expand later.
When you flip it the sock back out, you should have a finished seam to create the continuous length of socks.
Repeat as necessary.
When you have two sock tubes, flatten them out and align together.
Sew one edge to join the two sock tubes together.