What is the difference between Ethylene Glycol and Propylene Glycol?

What is the difference between Ethylene Glycol and Propylene Glycol?

Propylene Glycol has a slightly higher viscosity, a slightly lower heat transfer efficiency, does not perform quite as well in colder temperatures as Ethylene Glycol, however the advantage of Propylene Glycol over Ethylene Glycol is a lower acute oral toxicity.