A materials science lesson in Football
This picture is from the Miami vs Kansas City game over the weekend.
Modern football helmets are made from polycarbonate.
Polycarbonate, like all polymers, has a ductile to brittle transition temperature (DBTT). A temperature at which the material turns brittle like glass.
For polycarbonate, that occurs at roughly 0°F.
There is a test of fracture toughness, called an Izod impact test, in which a sample is struck with a hammer on a pivot, accelerated by gravity.
https://www.youtube.com/watch?si=x_4uVBex1cdrgdRo&v=1O1Q4vDOsxc&feature=youtu.be
Izod data for polycarbonate is available.
You can see how much less force it takes to shatter polycarbonate at low temperature.
The temperature at kickoff was -4°F, one of the lowest in NFL history.
A tackle is a high impact event.
A high impact at low temperature causes brittle fracture.
Now consider this in cold weather when you use polymer magazines.
The Marines chose not to adopt PMags because of cold weather testing.
There are many documented examples of other polymer mags failing in the cold, cracking when dropped.
You may love your PMags, but if it gets cold where you live, consider having a selection of metal magazines for cold weather. Aluminum doesn't ungerdo brittle transition at low temperatures.