Peak is the pioneer and market leader in the safer propylene glycol (PG) antifreeze category. Sierra antifreeze or coolant is formulated with PG rather than ethylene glycol the base for traditional antifreeze. Because of its PG formula, Sierra antifreeze is less toxic and therefore safer for people, pets and wildlife than conventional antifreeze. It is a premium automotive coolant that provides excellent freeze-up and boil-over protection and outstanding corrosion protection.