Three ways of heat flow, three ways of losing heat.

Most (of my) questions are about R-value which, correct me if I’m wrong, about a combination of conduction and convection.

But what about radiation? I guess foam and bats also stop radiation, but reflective film is better at it.

If so can something similar to R-value be calculated for reflective film?
If reflective material really works I wonder why most bats have none reflective paper.