Step 1: What You Need
Mats (I used the classic English bar mats)
Step 2: How to Proceed?
Spread a mat above the other.
I recommend sewing just under the flap of the pad.
Begin to sew the 2 long sides.
Now sew also one of the shorter sides.
(I used the fishing line because it is more durable than cotton and is also transparent)
Step 3: Turn Over
When you have finished sewing the three sides, facing the mats as if they were a sock.
Step 4: Filling
Now fill the bag just created with the foam (I used an old pillow).
I suggest you press each time you add foam so the pillow will become more swollen and soft.
Step 5: Close
Turns on themselves the two edges of the pillow.
To stop everything and be able to sew quietly, it temporarily freezes the two edges with clothespins.
Step 6: Et Voilà ;)
This is the final result.
You can use other types of fabric to your taste.
Let me know if you like it :)