Corn plastic

Plastic made from corn is hyped as an environmentally-friendly alternative to standard PET plastics. One of the claims about it is that it is biodegradable and can be composted.

As Boing Boing explains, it can -- under the right conditions. And those right conditions involve being heated up to 140°F (60°C) for ten days straight. In ordinary home composting, even after six months the plastic is unchanged.