Here's an easy way to use an old, ripped pair of pants to make a drawstring bag for your yoga mat.
Check this project out on Make: Projects
1 pair unwanted pants
several straight pins
1 safety pin
Estimated time: 1 hour
Step 1: Assess Your Pants
Are the legs wide enough for your yoga mat? Long enough with some extra space for seams? It's important to verify this before we go any further.
Step 2: Cut the Tube and Straighten It
Even straight-leg pants have some change in shape along their length, so turn the leg inside-out and pin and sew the flared part(s) to make a straight tube. Cut off the excess fabric leaving a reasonable seam allowance (1/4 to 1/12 inch).
Step 3: Create a Strap
This bag's main purpose is to allow you to carry your mat on your shoulder, so a strap is essential. Cut a length of fabric from the as-of-yet unused leg of the pants to match the length of your tube, and fold it over in a manner that hides the fray-able edges. Sew.
Step 4: Sew the Bottom Seam
We're going to create a pleat at the bottom that will make a less boxy shape at the end of the bag. with the tube still inside-out, fold the edges in on themselves like in the picture, and sandwich one end of the strap into the bottom seam (with the long side inside the main tube). Pin and sew (you may want to sew several times for reinforcement).
Step 5: Create the Drawstring and Casing
Test your bag to see how much space you have at the top to create the drawstring casing. With the bag still inside out, fold down a hem to match the size of your drawstring (a little bigger to allow movement, of course). I used the hem of the pants, so I didn't need to fold it under to hide any edges, but depending on the type and condition of your pants, you may need to turn the hem twice to make it nice. Leave a space unsewn so that you can thread your drawstring later.
To create the drawstring, use the same principle as the strap. I used the double-stitched seam from the other pant leg because I like the way it looks, and it's very strong.
Step 6: Thread the Drawstring and Attach the Strap
You're almost there! Thread the drawstring through the casing using a safety pin. Cut a hole along the casing on the on the outside of the bag. You can choose to embroider around this hole if you're worried about fraying, but it will only fray a little if you're using denim or corduroy, like me. Stick the two ends of the drawstring through this hole.
Turn the bag right side out and attach the loose end of the strap to the loose ends of the drawstring with the sewing machine. Be careful, as this will probably be very thick and could pose difficult to run through your sewing machine. I know my machine certainly didn't like it! Reinforce this seam.
Step 7: Go Do Yoga!
Insert mat into bag. Your'e on your way!
I'm still having problems with this step, but hey, I can't complain that my mat is too hard to carry around anymore! Need clarification? Ask a question in the comments.