best greenhouse phase change materials

[flplantguy]

We all know water has a good capacity for latent heat, but im wondering what other materials are better for it and more space economical. Use of water barrels is good but space is used up, and there are other types that are small in volume but i know nothing about them.  What other ways are there to raise the temp in a greenhouse at night passively?  Concrete floors are helpful also but not an option yet.  I read about parrafin wax, but didn't see if it was a good option for a greenhouse to add ten degrees to the low overnight, just that it is used in other applications. Does anyone know of a good material that takes little space that can be used in a greenhouse as described?

[happypalms]

Try rocks for thermal mass. Two layers of greenhouse plastic. Place plants on styrofoam to help insulating from the ground. No droughts of cool air.