I am looking for some advice about the strength of cars, such as in a crash. I have been told that for a car to be strong, the most important sign of this is that the car must have heavy doors.

Surely this cannot be right as cars are being made lighter for efficiency. As far as I knew, the ncap tests were what counted for how strong a car is, rather than if it has heavy doors.

I have a family member who insists that their car is 'better' than mine because theirs (in their opinion) has heavier doors. Both cars have 5 ncap stars but some people just don't listen, so if I had some facts about which parts of the car have the strength.