The material type and hardness is really up to you. We have used both urethane and silicone for compaction rollers, and we also use a range of hardnesses from around 30 to over 70. My personal opinion is that you want to use as hard of a roller as you can, and still have enough conformability so it will match the surface on which you want to place material. So, the flatter the surface, the harder the roller can be.