To eliminate the possibility of misrepresentation, I propose we construct barbells out of the densest practical material. While metallic hydrogen has its theor

To eliminate the possibility of misrepresentation, I propose we construct barbells out of the densest practical material. While metallic hydrogen has its theoretical attractions, you'll definitely need to buy some new gloves to lift. Uranium is reasonably cheap really, but export is a hassle. Perhaps something like an organometallic ceramic osmium compound? (Or have the aliens not officially released that to us yet?) Actually a block of wood will do fine. Or vinyl. Brass. Iron. Gravel-filled. Water-filled. Lead shot filled. (Not RoHS). Weight plates have a few standard sizes used in competitive gyms but it's not really standard in any way beyond that Olympic sequence. And at the end of the day the best weight is a weight you have and you can grip well :)