I needed some foam for a project, i am doing. So i went to Lowes (home depot sells it also) and got a $6 can of urethane spray foam. Tip: you can clean the sray tube and can nozzle by dunking them in acetone right after using them, this will allow you more than one use out of the can and straw.
acetone won’t disolve the foam once it has cured.
Also this stuff grows by about 50% when appliing.
So anyways here are my “findings”. the foam is as soft as a loaf of Wonderbread. 
Green floral foam is more dense than this stuff is. Green floral foam is also easier to cut and can be sanded. You won’t be able to sand this spray foam. Imagine trying to sand on a loaf of wonderbread.
It has many many small air pockets thru the foam.
Ok now the good part. If you are say building a plug for a car body this stuff would probably be very good for that provided you are using a skeleton of wood and filling the spaces with foam. Then just lay down some 3oz fiberglass cloth and wet it out with Epoxy only. Now you would have a surface to work off, of. I personally would do more than just one layer of 3oz glass though just to make it more sturdy. then start adding your fillers, etc to perfect your plugs shape.
But if you want something that cures solid… this foam is not it. You would probably be better off with a pour foam and check the mfg label for the shore hardness because that matters when it comes to shaping,etc.
I worked with a urethane foam chemist, foam can be modified to poroduce different hardness’. soft as bread as i see here, or hard and a million different hardness’ inbetween depending on how it was formulated.
and after writing this my dumb a$$ just remembered i have some blocks of urethane foam i got from Werksberg. That’s what i should have used. duh.
