I've had this cheap document bag (from some conference) for a few years. The zipper pull had a loop that broke off last week. I decided to try something new. The result is this zipper pull.
Step 1: Tools and materials
The zipper pull is made of nylon cord with a sleeve of plastic tubing. I used 3mm accessory cord and plastic tubing used for oxygen masks. Any clear (or coloured for that matter) tubing should work. Most aquarium stockist or hardware store should have it. Make sure that the inner diameter of the tubing is close to the diameter of the cord. The fit should be snug but not too tight.
For tools you will need scissors (or a sharp knife), a lighter and a short length of nylon cord that can be pushed through the plastic tubing with ease. It should be longer than the length of tubing you will cut (see later step).
The lengths given here are what I used and worked well for my particular zipper and gives a loop through which a finger comfortably fits. You may want to experiment with different sizes.
Step 2: Cut cord and tubing
Cut the accessory cord to a length of 17.5cm (or 7 inches). Cut the tubing to a length of 12.5cm (or 5 inches). The difference of 5cm (2 inches) is about the minimum you need (for 3mm cord) to still get the zipper pull through the eye of the zipper.
You don't need to heat-seal the end of the cord yet.
Make sure that the thin cord is longer (at least 5cm (2 inches)) than the tubing.
Step 3: Join two cords
Melt one end of the accessory cord as well as one end of the thin cord and join together. This may take some practice. Be CAREFULL as melted nylon can get very hot and can burn. The joint should be be made fairly strong.