To my knowledge, spending 30 points in fortitude will increase your hyper and hypo by 50 insulation points without armor, vitamins or parrot. Vitamins will increase fortitude by another 30 fortitude points so + 50 insulation points to the first 50 insulation points = 100 insulation points. Parrots supposed to increase fortitude per its actual level but to my knowledge that number is unknown. Some say it scales with the parrot's melee attack. For science, we are going to say another 30 fortitude points making our insulation points = to 150 points.
Now we need to talk about armor. We can have cloth which will provide insulation against heat and cold, fur will give insulation against cold and negative heat. The plate armor is similar to fur but mostly for melee.
Cloth armor New armor stats including the above 150 points of insulation.
Hypo = 29 179
Hyper = 60 210
Fur armor
Hypo = 216 366
Hyper = -130 20
The Plate
Hypo = 47 197
Hyper = -42 108
Be mindful that the above numbers are not fortitude points and are actual insulation points.
Meaning the following: wearing gear, having the equilibrium boost, placing at least 30 fortitude points into fortitude and having a parrot on your shoulder will provide you approximate numbers reference Hypo and Hyper insulation mentioned under "New armor stats including the above 150 points of insulation."
Anyways, the point of all this was that I make sure that I have at least 60 points in fortitude, 700 weight and the rest in health and stamina.
Warning: All information mentioned above is taken either from Atlas Wiki or in-game statistics.