Silicone grips (often called gripper dots or strips) are small silicone patches on the inside of the knee pad that create friction against your skin or base layer. Their main job is keeping the pad from sliding down your leg or rotating out of position while you ski—especially important during active turns, hikes, and falls.
This grip system hits the sweet spot for most skiers. It's secure enough to keep pads in place during aggressive skiing, but much more comfortable than rubberized bands, which can feel tight and leave marks on your skin. That's why you'll find silicone grips on most mid-range to high-end pads.
One thing to keep in mind: silicone grips work best when they have direct contact with skin or a snug base layer. If you wear loose layers underneath, the grip can't do its job as well. For most resort and freeskiers, silicone grips are the way to go—they stay put without feeling like a tourniquet.