I have a stash of home decorating fabric and have been wanting to make one of these for so long. There are plenty of patterns on the internet for drawstring backpack bags, so I won't claim this one is unique, although I used ideas from several different patterns. I'm going to provide the entire instructions here, but if you get lost, the closest one to mine is Skip to My Lou's drawstring pattern. I also should explain that I was on such a roll during the making of the first bag that I forgot to write everything down or take all the pictures. So, I had to make another bag - shown below. Here's what I used to make a 12.5" x 16" lined bag:
2 13 x 16" pieces of Fabric A (outside of bag)
2 13 x 16" pieces of Fabric B (lining)
2 3 x 12" pieces of Fabric A (casing)
2 3 x 12" pieces of Fabric B (casing)
2 2 x 3" pieces of Fabric B (tabs)
4 yards of cord cut in half (I used 3/16" nylon coated)
You can use any cotton fabrics, although I like using the heavier home decorating fabric, especially for the outside of the bag. You can also line your bag with a more water resistant nylon fabric, which makes it great for swim gear. The cording you can buy at a hardware store. You can also use ribbon (especially if your bag is lighter weight cotton), or you can make your own straps from fabric.
To begin the bag, you start with the smallest fabric details and work up to the larger bag. On this bag I decided to go fancy and make pockets for the inside. (I didn't include fabric measurements for pockets above. Just cut rectangle of outer fabric to whatever size you want your pocket and add 1/2" to length and width for hems.) I made 4 pockets, including some with Velcro closures and one for my sunglasses. For each pocket, hem all four sides of the fabric before you topstitch it to one of the large (16"x13") lining pieces. I sewed the pieces of the Velcro on the inside of the rectangle pocket and the other on the liner fabric, respectively. I also sewed a button on the outside of the pockets for decoration.
On the 2 x 3" pieces, fold the long sides over to the center so they slightly overlap and sew a seam down the center of the long side with a zigzag stitch. Repeat with the other 2"x 3" strip.
Pin the 13 x16" pieces of Fabric A right sides together. Fold the 2 x 3" tabs in half with the short ends together, and pin each one between the 2 large outer fabric pieces, up 1" from the bottom of the long sides. Keep the raw edges together.
Sew on three sides, keeping one of the shorter sides of the fabric completely open. I used a zigzag stitch throughout because home decorating fabric tends to fray. After ironing the seams, turn this "outer bag" right side out. The top of the bag is the end with the raw edges.
Now you are ready to sew the 13 x 16" Fabric B pieces with the right sides together. This time, however, leave a 3" gap or hole in the bottom short end for turning the bag inside out later. When you finish with the lining pieces, you will have both long sides completely sewn, the short end at the top of your bag will be completely open, and the other short bottom of the bag will be sewn closed except for a 3" gap in middle of that end. Iron the seams, but keep this "liner bag" inside out.
Next, make the 2 casing pieces by matching the 12 x 3" fabric pieces together, right sides facing. Use one of Fabric A and B to make each casing. Sew three of the sides, leaving one of the long sides completely open. Trim the corners, turn right side out, and iron. These are the casings from the first bag I made:
Now fold each casing on the long side so the liner fabric is on the inside of the fold. Here are the casing pieces I made for my second bag. The one on the left is already folded in half. These will be the casing for your drawstring and they attach to the top of the bag.
Center each casing piece along the top of the "outer bag," matching the raw edges together. The length of the casings is shorter than the width of the bag, so there will be 1" gaps between the ends of the casings and the sides of the bag. Center and pin the second casing to the other side of the "outer bag." You are now ready to slide the "outer bag" with the casings pinned into the "liner bag." The "liner bag" is still inside out, but the "outer bag" should have the right sides out as you slide it into the liner bag. All raw edges should be aligned. The right sides of the fabric will be together, but all you will see is the wrong sides of the fabric (see picture below)
Sew all the way around the opening, sewing together the "liner bag," the casings and the "outer bag." When it is all sewn up, it will look like this (you are looking into the top of your bag.)
Flip the bag to the bottom and you can reach in and pull out the "outer bag" through the hole in the bottom of the "liner bag."
Once you pull the bag completely out through the hole, you should see the right sides of the fabric like this:
Pull the casings to open the bag and push the liner into the bag. It should look like a real bag without the drawstrings! Now you are ready to thread the cording. Take the first cord and thread an end through one of the tabs near the bottom of the bag. Continue up along the outside edge of the bag to the ends of the casings at the top of the bag. Using a safety pin on the end of the cord to guide you, thread the cord through the back casing to the other side of the bag. Continue around the bag through the other casing, guiding it through the casing back across the top of the bag to the side where you started. As the cord comes out of the casing, guide it back down the side of the bag and back through the original tab. The ends of your cord should now be together, and you can tie the ends in a knot so it won't slip out of the tab.
Repeat the process with the other cord on the other side of the bag. Each cord will go through the casings from opposite directions. This is a picture of me threading the second cord into the back casing with the other cord already in place. You will probably need to burn the ends of the cord after cutting them to prevent fraying.
And that's it! It seems complicated, but it really is simple once you get the hang of it.