How much closed cell expanding foam insulation do I need?
According to the product's data sheet a 750ml can yields 43l.

I'm getting 0.86 square meters per can at 50mm thickness but I don't do stuff with the metric system often so I suggest you double-check my numbers based on the data sheet and see if we agree.

As to if it will keep you warm or not, that all depends on your heat source.