Urethane Foam Variables

[Hudson Force]

I've had some great experience with successfully replacing some wet balsa core with some sheets of end grain balsa tiles on a cloth matrix. I will continue with my technique in dealing with some more soft spots; however, there are some spaces where I would choose not to cut away the full top laminate and decide to pour a two part high density foam into these places. When shopping for these polyurethane two part foams, I see and understand the density variable, but I have not been able to notice any other variables in the products on the market. What are some comments from those with more experience? Are there any other variables among the two part, mix and pour, urethane foams that would be of interest for those replacing some damaged coring?