I wear jeans almost exclusively!!!
I have always had a time of wearing out knees and the bum area of jeans - too much crawling around on the ground! OK - I know people actually pay huge money for the look I end up with - shredded knees and such. Not this gal - I can't stand my knees poking through.
I don't like iron patches, as I have never had good luck with them sticking well. I just can't sew patches in place on knees with my sewing machine. I can't get them in the right position without bunching up and sewing something extra into the mended area!!!
Here is what I use.
This stuff is great and lasts and lasts. It can be purchased at most craft and fabric stores. Not only do I use this on jeans - but I have used it on crafts as well. We all have that project that is just an odd size or area to sew. This stuff is great and holds up very well wash after wash.
As you can see in this picture, patches can be small or large. The one on the left is the inside of a pair of jeans - knee patch. The one on the right is patching I did right in the zipper/crotch area. It was difficult working around the zipper and thick seams with sewing machine - sew I fused it!
I can always add a pretty patch to the outside of the knee or bum area with the same product.
I have used this product mending fabric purses, jeans, and craft projects. I have 'fixed' small rips in the seam of pillows, without removing all the stuffing. I have applied appliques to items easily. This works wonderfully on any oddball area and on all kinds of fabric.
My neighbor called a month or so ago, asking for suggestions on attaching fabric to a chair she was recovering. She used this to get everything attached and set - them she added brads for a finishing touch. She called and said it worked so well, and that she would never be without it from now on (she doesn't sew).
I keep this on hand all the time. If kept properly capped a bottle will last for ages. I have a larger bottle (in stock) that I got several years ago when Hancock Fabric went out of business. I don't ever want to be without it.
If you have never tried it (or any product that is similar), think about giving it a try. Some areas sell a product called Liquid Stitch which is the same thing.
Hopefully this tip will help with your odd mending and craft projects.