I do a lot of cutting and welding on the ground and I dont wear any. I found they make a good spark catcher and that dont feel to good. I usualy jist put and old pair of welding gloves on the ground and neal on those if I am going to be there a while. A friend of mine that was a carpet layer use to have leather patches sowed on the knees of his jeans and that seemed to help a lot, might be a good option for welding allso.
Tom
We use kneepads that are covered with leather except for the hard plastic cap. They have the elastic top strap and non-elastic lower strap and are made a bit wider than the ones you usually find in Home Depot. I looked my pair over for a brand name but there wasn't any that I could find. However, I'm sure if our welding supplier can find them, others can too.
I've also tried the foam pads that are sold for use as elbow or knee pads that are covered in a stretchy Ace bandage kind of material. I use them underneath my pant legs for when I might only need to briefly crawl under something -not for hard use.
I used to not pay so much attention to padding for the knees but I'm getting older and I've seen too many folks mess up their knees from abuse. And nothing gets your attention quicker that planting the knee cap squarely on top of a small, hard object.