Bringing your lunch to school or work is green: You might prefer to tote...

A fleece blanket, an artist's paint, an airplane windshield. What these things might have in common is this synthetic, petroleum-based polymer resin. In the form of hard plastic (known by brand names Plexiglas and Lucite, among others), it is strong, clear, and shatter-resistant. As a textile fiber, it resists shrinkage, stains, and wrinkling. As a binder in paint it dries quickly and holds color well. But acrylic also has its downsides: Since it's petroleum-based, it increases our dependence on fossil fuels. It also burns easily. Its production exposes workers to toxic and potentially carcinogenic chemicals. And it is difficult to dispose of, as it biodegrades very slowly and recycling options are limited. Acrylic plastics are labeled with a 7 in the triangular recycling symbol, and few recycling programs accept them.

Mold isn't just a patch of blue to indicate your bread's gone bad. There are molds that grow on...