I put the last can on , it will expand for the 24hrs before I trim it again then I seal it and put it in place. Once its plumbed in I will stuff the area around the tub with some left over fiberglass insulation for a complete fill of the bathtubs area.
It will be as warm as a thermos ..I think
I am thinking about making a cellulose insulation concrete mix for the tub`s leveling bed for more insulation. Its r-value is reported to be within 2.0 and 3.0 per inch
http://en.wikipedia.org/wiki/Papercrete
http://www.livinginpaper.com/mixes.htm