My girlfriend and I learned how to sew and made an ultralight backpack.
My plan was to make a prototype bag with cheap nylon. After, test the prototype until most things break and build a second backpack with updates and higher quality fabric like cuben fiber.
Unfortunately, I didn't know it would take me 20 hours to learn how to sew and make a backpack. It is already very light so I'll wait until it breaks to build a new one.
The backpack only weights 310 grams! With lighter mesh, cuben fiber and compression cords, I am sure it could get below 250g.
The overall design is based on Christopher Zimmer's first pack, who released a backpack template for a pack like this in 2011. Now he sells custom made backpacks on his website. I spend a lot of time reviewing DIY backpack builds and patterns and his is the best. The custom packs he sells are my goal.
Zimmer also posted a tutorial with template on making simple straps. I didn't have chalk so I used flour. It made a mess but it worked! If I had to redo the straps, I would propably use a single thicker layer of padding mesh instead of two. Sewing the grosgrain around was the hardest part of this pack.
Every edge of the pack is seam binded using a grosgrain ribbon. This adds some structure to the pack, finishing, makes it more durable and adds some water resistance. Doing the corners with grosgrain was hard and ugly because I tried to do one piece of grosgrain most of the time. Next time I'll just cut it and do corners with two pieces or use round edges instead of 90 degree corners.
Next time I seam bind, I will 3D print a seam binding attachment like this:
After being done with my pack, I inspected my Osprey backpack and realized they use 1 inch grosgrain. Mine uses 3/4" and it would have saved me a lot of time to use the larger ribbon. With 3/4, I couldn't fit over some of the top mesh so most elastics knots aren't secured in the grosgrain. Use 1 inch grosgrain!
The Osprey backpack also never has triple corners (left illustration). All grosgrain corners are linked with straight or slightly curved grosgrain edge and always use only 2 pieces (left illustration).
As this was my prototype, I used 1.9oz coated ripstop. Second iteration would use superior Dyneema (cuben fiber) tissue ($$$). I found recommendations on tisues on this post of the Make Your Own Gear subreddit /r/myog.
I wanted to practice sewing and that's why I cut all fabric instead of simply using one long rectangle to use as front, bottom and back. It's a good test if I want to use different fabrics for front, back and sides but it was much more work.
The mesh is heavy but somewhat elastic and seems resistant. It is called "Lycra Micro Mesh". Next time I'll use regular poly mesh with elastics.
Use larger thread spacing and stretch the elastic mesh to sew it while keeping it's elasticity.
The bag is water resistant enough. It won't hold water and won't stay dry under heavy rain, like most backpacks. The grosgrain really helps but it's not perfect.
A seam sealer can be applied but it's not worth it.
For true water resistance, use a trash bag inside to carry items.
All materials are from Quest Outfitters and total cost for one pack is around 30$.