The RK3 HD is the next fin in the RK3 range of fins. The RK3 HD is made from a higher density material than the standard RK3, which makes the fin stiffer and heavier. The RK3 HD was developed in response to feedback from divers who prefer a heavier fin. The new compound of the RK3 HD adds weight to make it more negatively buoyant than the standard RK3. An ideal fin for dry suit diving.