What you'll need:
-Old bike tubes (26" or 29" are the widest. just ask for these at most any bike shop).
-Vinyl (I use old billboards. I called up Next Media and they gave me a few free ones).
-Lube (I use cooking oil because it's cheap, biodegradable, wipes off easy, and leaves a shiny coat).
-Most any sewing machine with a leather/denim needle and adjustable tension.
-Hot glue gun for tacking tube in place before sewing (optional, but makes it way easier/quicker. you can use clamps/safety pins too.)
You can check out some instructables I've made using these techniques:
The Wallet - Female
The Wallet - Male
The Side Bag/Purse
The Messenger Bag (INSTRUCTIONS COMING SOON)
Step 1: Preparing the Material
1) To cut the tube open into a a sheet of fabric, cut the valve off so the tube is straight, then pick an existing line near the inside of the curve of the tube and cut down it. Cutting on the inside prevents the material to curve to one side or the other.
2) Once the tubes are cut the long way, I straighten out the ends by taking a 90 degree angled ruler, lining it up with either end, drawing a chalk line, and cutting.
*Note: Exactly measuring bike tubes in general will drive you crazy because they will probably end up stretching a bit. I usually estimate and measure everything to itself along the way using as much of the material as I can. Reuse!
1) Old billboards have a tiny grid system all across it. I usually try to cut along these to keep my lines straight.
Step 2: Sewing the Material
1) line two tubes up next to each other the long way
2) overlap tubes about 1/2". I usually use an existing line on the tubes for good measure.
3) use your hot glue (the best), clamps, or saftey pins and tack the tubs together every 2-5". If you skip this part, you're machine will probably stretch the tubes unevenly when they're being run through the foot.
4) lube up the top of the material. I usually use a paint brush, but a finger works too. Don't be modest!
5) run through the sewing machine (test for tension first by using some scrap material). I use a normal straight stitch, but if your machine can do 2 front 1 back that might be strongest.
6) wipe the lube into the material with a rag - this gives the tube a nice shine. use more lube for a nice coat,
To sew tubes to vinyl...
1) lay tube sheet on vinyl, trace, and cut to size.
2) tack material, lube, and sew (same as above).