Exercise Mat material creation -- 2

I am looking for a durable, water and odor resist material that can absorb energy(identical to dry sand) from a persons movement. the dimensions length: 68in by width: 24in. By 1.5 in or 1in thick if possible. The material needs to mimic the same properties dry sand does when a person runs, moves, or jumps on it . Sand absorbs the energy from a person while minimizing the force of energy transferred back into the person. Basically, I would like part of the mat to consist of sand if possible but since sand is to heavy I am looking for material(s) that is lighter than dry sand and can preform close to the same functions dry sand does regarding the transfer of energy. Polymer gel, plastic, or anything that can be used to create this function would be great. A mix of sand and other substances would also be considered if possible. That mat does not have to consist only of one material. Could be a combination of foam or other ingredients. Don't necessarily need the mat created but an outline of what materials I could combine/use to achieve the effects desired. Also, The material would have to be light, as the Mat can not weigh more then 7 pounds but the goals is to keep the mat at 5 pounds of total weight.