Antifreeze

[Langstone]

What is the difference between propylene and ethylene based antifreezes?
Why would one use one or the other?

[Clanad]

There are several technical differences, but both do a good job of freeze point depressant as antifreezes. However Propylene glycol is not toxic to animals or humans, which makes it more attractive since Ethylene is highly toxic and deadly if taken internally...