I read about a sleeping bag you make with two "space blankets" does anyone have any idea if it would work.I mean it would be light but would it be warm

What do you mean by the word "work"?

Will it keep you alive in an emergency? Maybe.

Will it keep you just as warm and comfortable as a real sleeping bag? Definitely not.

You have to give something to get something. Everything is a compromise. This "sleeping bag" is on the extreme end of the spectrum where comfort is all but eliminated to save weight and cost.

It sounds like a great idea to me.........as long as I don't have to sleep in it.
If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.