I have a couple pairs of Fjallraven Vidda Pros, and they have double knees with an opening to slip a foam pad inside (which they also sell). Carhartt has a simi

I have a couple pairs of Fjallraven Vidda Pros, and they have double knees with an opening to slip a foam pad inside (which they also sell). Carhartt has a similar method with their work jeans. I’m sure this could be DIY’d as well for the sewing-machine-inclined.