As someone who tries to be environmentally conscious when possible, I started dabbling around and looking into the differences between Polyethylene and Ethylene coolants. Yes I know it's a closed system and environmental exposure is minimal. However, in the U.S. alone there are roughly 250mm registered vehicles with 270mm registered drivers. Let's assume most coolant systems hold an average of 5gal, we're talking about 1.25B gallons of coolant on roadways. If annually there are 6mm accidents, and let's say 40% end up with a cracked radiator, we're looking at roughly 500mm gallons of spilled coolant. Based on what I can find, there doesn't seem to be a difference between the two from a compatibility standpoint. When it comes to practicality, there are some physical differences between the two with regards to heat transfer and freeze rating. But even then, it's not that different. For example, Prestone Extended Life has a freeze rating of -34*F and boilover rating of 265*F in a 50/50 mixture. Meanwhile, Prestone LowTox has a freeze rating of -26*F and a boilover rating of 229*F in a 50/50 mixture.