What is polypropylene, the chemical burning at ExxonMobil Baytown?

HOUSTON – A massive fire is burning polypropylene materials Wednesday afternoon at the ExxonMobil Baytown Olefins plant.

Officials said the processing unit on fire contains a light hydrocarbon mixture of propane and propylene. 

Here's what we know about polypropylene, the chemical that officials said is burning:

Polypropylene is a high-performance, lightweight durable plastic used in automotive, appliance and packaging and labeling.

"Polypropylene delivers performance and sustainability benefits to produce a wide variety of consumer products," Cindy Shulman, ExxonMobil's vice president of plastics and resins, said on the company's website. "It's a versatile material providing high impact resistance and high stiffness to lightweight applications. It is safe, can be recycled and requires less energy to produce when compared with other plastics."

Polypropyelene is "a white, mechanically rugged material and has a high chemical resistance. Polypropylene is the second-most widely produced commodity plastic after polyethylene," according to Wikipedia.