Like other tubeless tyre inserts, Rockstop is designed to protect rims from dents and tyres from pinch flats, but it’s made from a polyurethane-based elastomer rather than the usual foam.
The first advantage I noticed is that it doesn’t absorb any tubeless sealant, so you don’t need to add extra. It’s quite heavy though, at 270g per insert for the 29er version, which is designed for rims with 23mm to 35mm internal widths. That puts it on a par with the most robust inserts, such as CushCore (265g).
Installation is easy, with the large holes meaning that there’s no need for special valves because the insert won’t plug the valve when pressure is released.
The insert takes up little space inside the tyre and so has no discernible effect on the ride feel in normal conditions, unlike CushCore, which gives a more damped feel over rough terrain.
There are only a few millimetres of material covering the rim sidewalls, but because the material is tough and rubbery it appears to provide meaningful protection, as well as muting the clanging sound when banging into rocks.
My sample remains free of damage after months of use, while many foam inserts become cut, torn and stretched over this timescale.