The Biodegradable Products Institute

The Biodegradable Products Institute, based in New York, evaluates and certifies materials and products that can become compost.

http://www.bpiworld.org/BPI-Public

I recommend checking out the list of materials that have already been approved (divided in categories) as well as reading through their criteria:

http://www.bpiworld.org/BPI-Public/Approved.html

They even have a specific logo that is applied to the approved products, to make sure people know these are biodegradable.

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