Some trousers have inverted pockets at the knees for the insertion of knee pads.

flintronic Knee Pads Work, 1 Pair 20MM Thick Knee Pads Gardening, Protective Knee Pads for Men Women, Anti-Slip Collision Avoidance Knee Sleeve for House...
4.0

IPSXP Professional Knee Pads for Work,Gardening & Construction Knee Pads for Men and Women with Thick Double Gel Cushion, Strong Adjustable Non-Slip Straps,1...
4.0