A couple of rings built around titanium bands. The titanium core adds durability, keeps it hypoallergenic, and cuts down on the bulk compared to a solid wood band.
The zebrawood one is made from a thick shaving off a glued up zebrawood panel wrapped around the band. The striping in zebrawood makes it a natural fit for this kind of thing.
The walnut and maple one is a laminated build, dark walnut on the outside with a maple stripe running through the middle. Two very different looks but the same construction approach underneath.