Over-layer knee pads are designed to strap on right over your ski pants, making them super easy to slip on and off between runs. This is why they're the go-to choice for race skiers who need to quickly adjust or remove their pads at the starting gate without stripping down.
Another big advantage is adjustability—since they sit on the outside, you can reposition them easily if they shift, and the straps are built to accommodate the bulk of your outer layers. You'll always get a secure fit without fighting against tight ski pants.
The trade-offs? They're visible on the outside of your pants, which some skiers don't love aesthetically, and in deep snow, the edges can catch and collect snow. If you want a streamlined, hidden look or you're mostly cruising groomers recreationally, under-layer pads might be a better fit. But for racers and anyone who values quick on/off convenience, over-layer is hard to beat.