If you are buying new fabric, if you are using brand-new never-before-used nylon, great! You can skip this step.

Otherwise, welcome to my favorite step! Get comfy. This is the time consuming one.

The reason I wanted to make a backpack in the first place is because of this blue trench coat, pictured above. Yes, that one. I have had this trench coat for ten years now and I love it to pieces. Do I ever wear it, you ask? The answer is a resounding no. I saw this trench coat in Burlington Coat Factory when I was fourteen and fell in love with the color (a blue so intense it doesn't really even come across in this photo). The fact that it was a size 14 petite did not stop me from forcing my mother to spend the $30 to buy it for me. And while I am many things, I am not and never will be a size fourteen petite, so I can count on one hand the number of times I've worn this coat. (It's currently disassembled, seams picked apart, waiting to become a backpack.)

If you're making a backpack from a trenchcoat, great! Trenchcoats are often made of four or five yards of fabric and are usually made of more sturdy and weather-proof fabric great for backpack exteriors. However, you will spend a lot of time prepping. Get a seam ripper, and get familiar, because you will spend a lot of time ripping out all the seams in this trenchcoat, and tearing it into five or six pieces (two back pieces, two front pieces, two arms, and liner). The great part of using a trenchcoat is that there are so many really cool things you can add onto your final backpack--epaulets become useful compression straps on the sides! Former trench coat pockets can become secret pockets sewn into the side seams! There are so many buttons! And the lining makes a really cute lining for the backpack itself, if you don't want to have a fully waterproof lining like the rest of this instructable.

As for other thrifted fabrics, go crazy! Find some interesting curtains, or some normal curtains you think would look good as a backpack (see my green curtains with gold and crimson embroidered flowers, which became two beautiful backpacks). Use duvet covers, overcoats (tweed backpack, anyone?), wool suits (hella stylish wool backpack yes please), old leather jackets (but beware sewing leather unless you know your sewing machine can handle it). I love looking through coats and suits at thrift stores--two often-overlooked sections with a gold mine of fabric choices and often high quality, natural fibers. It's much easier than you think to find wool and silk and linen when you're looking through all the disregarded suits!

Don't forget to look for other materials at thrift stores, too. Buying new nylon runs anywhere from $1-$3 a yard; in contrast, ugly duffel bags with yards and yards of nylon are just $3 each at the goodwill. Look for big pieces of luggage that have lots of nylon, lots of buckles, lots of triglide adjusters. Bonus points if they're ripped and aren't useful anyway! I got all of my nylon and buckles from a weird piece of molded plastic which was designed to hold a boxy, 90's television. Goldmine. And don't be afraid to branch out--the floral backpacks don't use nylon webbing at all, but instead the straps themselves, the webbing holding straps to bag, and the webbing which holds the rolltop closed are all woven canvas belts, which are easy to find at every thrift store, come in a variety of widths and lengths, and each one comes with its own closing mechanism. Don't like plastic safety-vest style buckles? Find belts with stylish buckles and add some vintage charm to your backpack.

The beautiful thing about making backpack is that you can make backpacks out of whatever you want. Make chevron backpacks, make floral curtain backpacks, make teal backpacks, make pinstripe suit backpacks, make quilted down backpacks! I just wish I could restrain myself, because now I want to make backpacks out of every mildly interesting pattern I see at the thrift store.