How the hell do environmental resistances actually work?

So, I am on a cold planet right now. It says it is -18 degrees Celsius on the scanner and I keep getting frostbite and hypothermia effects from it, despite having 45 thermal protection assuming these all stack from each piece of my suit (suit, helmet, pack).

Am I maybe missing a way to see what the actual environmental damage threshold is? How the hell am I supposed to protect myself from this shit? Is that not what the 4 items (thermal, airborne, corrosive, radiation) below the DR are meant to protect against? It's like everytime I am on a planet and it doesn't show my civilian clothes, I'm constantly up against these environmental effects. Getting burns and blisters from the heat, radiation sickness from lack of a magnetic sphere, getting sick from airborne diseases... I've been putting as much into these resistances as I can and it doesn't seem to help.