These pads aimed at dirt jumpers have plastic inserts rather than just the usual padding, meaning if you come down hard or end up sliding on your elbow, they can take a fair whack and they won’t slide off your arms.
They’re held on with grippy silicone inside the top of the pad, then a strap as well as more silicone around the forearm. They might not be too comfortable to chill-out in, but they feel fine on the bike.
They allow plenty of arm movement and didn’t slip down when we were riding. Once you’re holding the bars, the plastic protection is in just the right place.