Their pellets are hard due to the extreme pressure of the extrusion process, and a very low moisture content. I don't find their sinking pellets to be any harder than say Northfin pellets of similar size, or Omega pellets that I have used. Most sinking pellets of quality are dense, those that aren't typically have higher starch content so they soften up once they hit the water. Moisture invites mold, so every manufacturer tries to keep moisture content under 10%, some manufacturers shoot for half that.