Here are basic instructions for making a laptop sleeve out of FedEx envelopes. I was looking for a strong and waterproof material to make my own sleeve from and remembered that FedEx and the US Postal Service both use Tyvek (or similar) material for their envelopes. My sleeve fits a MacBook, but the design is easily adaptable for other sized laptops.
Step 1: Materials
Find yourself 3 or 4 FedEx envelopes. This sleeve takes 3.
Step 2: Padding
Cut your padding material to fit the inside of the envelope. I used felt. Then stuff it into the envelope.
Step 3: Trim
Trim the adhesive flap from the bag.
Step 4: Mark Dimensions
Mark the size of the sleeve. *Note* Leave some extra room on the sides and top (1/4-1/2") for the thickness of the laptop and the seam allowance).
Step 5: Sew Pocket
Pin and sew along your lines and along the opposite side edge (shown right). This leaves an opening for the laptop (bottom).
Step 6: Trim Seems
Trim the seams.
Step 7: Turn Inside-out
Turn the pocket inside-out. This is the basic sleeve without the flap.
Step 8: Start Flap
Measure and mark the width of the folding flap.
Step 9: Pin Flap
Sew the flap to size and trim the seam. Pin the flap to the inside back of the pocket. You may notice that I mistakenly sewed it to the front on my first attempt (sigh).
Step 10: Attach Flap
Sew the flap to the pocket. I also sewed around the top of the pocket to hold the padding in place.
...yes, I am using red thread on the spool and purple on the bobbin. So what, I liked it.
Step 11: Fold Flap
That's basically it.