I've been watching a new feature on Salon.com called "Ask Pablo," where readers can send questions to Pablo Paster, a sustainability engineer. Today's question is plastics related: Should I buy soda in plastic bottles or aluminum cans?

This is a interesting question, and Paster breaks down a lot of numbers, including the energy needed to make both types of containers, recycling rates, greenhouse gas emissions and shipping costs. In the end, he favors PET over aluminum.

Let's assume that both beverage containers are filled in the same facility and shipped to the store with the same truck. The bottle weighs 2.05 kg when full (2 liters plus 50 g) and the 5.6 cans weigh 2.084 kg (2 liters plus 84 g). This means that the cans require slightly more fuel to transport than the bottles. That's two strikes against cans. How about a third strike? Soda bottles often find a second life in my favorite winter garments, as some clothing brands manufacture fleece in part from recycled plastic, which is melted into pellets and extruded into fine fibers. Try doing that with aluminum.

Paster has tackled quite a few plastics-related issues in recent weeks, including a column on bottled water and an explanation of plastics recycling.

The most recent column generated quite a bit of reader response to Salon's Web site (although not all of the writers very well informed). If you're interested in what the public thinks about plastics, this is a good Web site to monitor.