I didn't care if it looked original or not--it's not like I'm restoring a classic car--so I decided to use craft felt instead of automotive fabric to save money. To save time, I decided to stitch the felt around the edges with a blanket stitch instead of trying to reverse-engineer the original construction.
The materials cost me just over $2, and the project took about 3 hours including buying materials.
Even if your sunvisors aren't falling apart, you could use this method to add some color or even customize your sunvisors with appliques or glued-on felt designs or letters.
I made this at TechShop San Jose (www.techshop.ws).
Step 1: Purchase Materials and Gather Supplies
72" wide craft felt (Measure the depth of your sunvisor, double that amount, and round up a few inches; mine took 1/2 yard) (1/2 x $4.99/yd)
1-2 packets coordinating embroidery floss (mine used slightly less than 1 packet, but your sunvisors may be larger or your stitches closer together) ($0.39 each)
Pen (for marking fabric)
A few pins
Screwdriver (to remove/replace sunvisors; check your car, mine needed a Phillips head)
Step 2: Cut Out Fabric
1. Remove your sunvisors from the car by unscrewing the screws with your screwdriver. Put the screws in a safe place.
2. Fold the fabric with the cut edges together, not the selvedges. (It will be a very skinny rectangle.) DO NOT TRY TO DOUBLE THE FABRIC AND CUT BOTH PIECES THAT WAY! I did this, and the thickness of the felt made the piece inside the fold smaller than the one outside the fold and I had to recut it. The fold should be at the top. Felt sticks to itself, so just smooth it flat with your hand and you won't need to pin it together for it to stay folded properly.
3. Lay one sunvisor down on the fold about 1/2" from one end. The top straight edge of the sunvisor (with hardware sticking out of it) should be 1/4"below the fold. This allows for the thickness of the sunvisor when you cut the piece.
4. Outline the sunvisor with the pen and move it aside. Remember to mark the slot where the hook above the dashboard catches the top of the free end of the sunvisor.
5. Draw your cutting line 5/16" outside the outline you just drew. This leaves just enough fabric to wrap around the edge of the sunvisor and leave a seam allowance for your blanket stitching.
6. Cut felt along the cutting line. Make your cuts as smooth as possible, as they won't be tucked inside.
7. Test-fit the piece of felt to the sunvisor and see if there seems to be an even seam allowance all around. If not, start over.
8. When you are happy with the way the felt fits, use the piece as a template for the other sunvisor. Place the marked side down so they will be mirror images and you can hide the marked side inside.
9. OPTIONAL: If you want to decorate the new covers with appliques or embroidery, do it now. (I didn't think of this until I was finished.)
Step 3: Sew a Blanket Stitch Around the Free Edges
1. Open the felt piece and lay it marked side up.
2. Place the sunvisor on the felt with the straight side at the middle of the felt. Wrap the other side over it and fiddle with the felt until the edges line up with each other.
3. Pin the seam allowances together at the corners and middle of the free side or pin them to the edge of the sunvisor.
4. Thread your embroidery needle with a comfortable length of embroidery floss.
5. Sew the edges together using blanket stitch. (See https://www.instructables.com/id/How-to-Sew./step7/Decorative-stitches/ if you aren't familiar with this stitch yet.) I did not bother stitching the felt at the slot on the top edge because I thought it looked OK the way it was. If you're wondering what to do when you run out of thread and need to start a new strand, I included a photo of how I hid the tail end of the old thread by leaving it long and tucking it between the felt and the visor.
6. Repeat steps 1-5 for the other sunvisor.
Step 4: Reinstall Your Sunvisors in the Car
Just take the sunvisors and the screws you saved, and screw them back into the original holes.