Resins can be made from source material besides oil and natural gas. There are a number of different ways this is done. The most common alternate source material is polylactic acid, which is derived from corn.
"[Companies that produce bio-based resins] take corn sugar and feed it to microorganisms that produce a waste product called lactic acid, which is the monomer," says UC Berkeley's Kingsbury. "You separate out the lactic acid and make it into a plastic."
But there are some downsides, especially with the use of corn. After all, corn requires the use of a lot of petroleum-based fertilizer to grow, and the runoff enters waterways, leading to the creation of so-called "dead zones" -- spots where oxygen is cut off -- in places like the Gulf of Mexico, imperiling marine life.
Kingsbury says a better alternative to corn is sugarcane, which uses the same basic procedure to produce resins but doesn't need as much land and produces fewer emissions during processing. But whether you're dealing with a corn or sugarcane-based resin, it's still important that the products they're used to create be disposed of properly.
Indeed, Kingsbury says that all too often, people see that a bottle or container is compostable and think it's just fine to toss it onto the side of the road. "A problem we run into is that people litter more when they believe it magically disappears, and that's the last thing we want," he says. "We want it in compost or recycling, not along the side of the road."