Seam weldng and foam filling chassis rails

[Limbo]

The stuff i got is semi hard. The outer layer you can stand on and it will not break but you can dig it out with a screwdriver. The inner bit is abit softer so not sure. What's the numebr of that plac ein seven hills? i wanna try some.
Also how much does 2kg make? that sounds like alot of foam