I have a pair of much loved, indestructible Polartec fleece pants which were my go-to winter pants for over 20 years. While the fabric is still in pretty good shape, the elastic broke down over time. After 20 years, my favourite pants were starting to fall down because the elastic waistband had lost its stretch! How to fix them?

This instructable shows you how I replaced the elastic waistband and fixed these pants so they fit like new. In this instructable, I use a serger, but I will also explain how this can be done using just a regular sewing machine.

This project is for elastic that is sewn into the garment. If your elastic is simply enclosed in a casing and not sewn in, it is much easier to replace - just find or cut an opening in the casing, remove the old elastic, thread new elastic in with a safety pin and sew the ends together.

Supplies

You will need:

A serger and a sewing machine, or just a sewing machine
1" wide elastic - enough to go around your waist
Measuring tape
A small piece of scrap fabric
A stitch ripper
Thread, scissors, pins and basic sewing supplies

Step 1: Remove Old Elastic

This was one of the hardest parts as the elastic was very securely attached.

If you don't mind the waist being about 2" lower, you could just cut off the entire waistband including the worn out elastic.

If, like me, you want the waist to be in the same place, you will have to take a stitch ripper and rip out the stitches that held the old elastic in place. This will usually be 2 rows of stitching. Turn the pants inside out and rip out the stitches using a stitch ripper.

Once you've removed the 2 rows of stitching you will probably find that the elastic is still attached at one edge with a serged stitch (see photo - I've use a blue fabric test sample to make this easier to see). It's easiest just to cut off the 1/4" or so of fabric that is serged to the elastic rather than trying to rip out these stitches. You are only losing about 1/4" of your pants fabric.

Step 2: Make New Elastic Waistband

Measure your waist and cut the elastic 1" less than this measurement.
Put the elastic around your waist with the ends just touching - does it feel too loose? If so, adjust it so that it feels just right, and cut it shorter if necessary.
Cut a piece of scrap fabric about 1" X 3".
Fold this over the elastic, with the cut edges of the elastic just touching, so that the fabric encloses the elastic on both sides and pin or clip in place. This technique, with the elastic ends butting up against each other, avoids the bulk which would result if the elastic edges overlapped.
Sew close to the edge of this fabric square, so that the ends of the elastic are enclosed and secured in place and you now have a circle of elastic. If you wish, try on this elastic circle to confirm that it fits comfortably.

Step 3: Divide the Pants Waistband Into 4 Equal Sections

The side seams of your pants already divide your pants waistband into 2 halves. Put a pin in each of the side seams at the waist.
Hold the pants so that the side seams (with your pins) are sitting on top of each other (see photo), and mark the 2 side edges with pins. You now have 4 pins dividing your waistband into 4 equal sections.
Take the elastic circle that you made in the previous step and mark it into 4 equal sections with pins or chalk.
Pin the elastic to the inside of the pants, approximately 1/4" from the edge of the fabric, matching the pins that mark the 1/4 sections of the elastic and the fabric.
Add more pins in between, stretching the elastic as you pin, so that you fabric is pinned to the elastic every few inches. The pins should point towards the top edge of the pants, so that they can be easily pulled out from the left as you sew. This ensures that the fabric will be gathered evenly into the elastic.

Step 4: Attach the Elastic to the Inside of the Pants

Serge or sew the elastic to the inside of the pants, pulling on the elastic to stretch it so that it gathers the fabric as you stitch and encloses the elastic in the overlock or zig zag stitch. If you are sewing, use a zig zag stitch or a stretch zig zag stitch.
Overlap the stitching once you are back at your first stitches and knot the threads so that the stitching is secure. If you used a serger, the serger automatically trims off the 1/4" of fabric that you left at the edge as you sew and you must be careful to ensure that the serger does not cut into the elastic. If you used a sewing machine, you can carefully trim off the excess 1/4" or turn it under.

Step 5: Fold the Elastic Down and Stitch in Place

Fold the elastic down so that it is on the inside of your pants and enclosed by fabric on both sides. Pin in place.
Stitch close to the bottom serged edge, using a stretch stitch or a zig zag stitch on your sewing machine.
Add one more layer of stitching, again using a stretch stitch or a zig zag stitch, close to the top of the waistband.

Step 6: Enjoy Your Newly Repaired Pants!

I intend to get another 10 years out of these fleece pants! I've been wearing them constantly since I fixed them and they fit like they did when I first bought them more than 20 years ago.

I will use this Instructable as a guide for replacing the elastic on other waistbands when needed and I hope you do as well.

Note: if you buy elastic and keep it on hand, you should mark the date on it, as all elastic breaks down over time. Store elastic away from the light as UV rays will speed the breakdown of elastic.