Oxo-degradable
Made from plain plastic and an oxo-degradable additive, these bags are designed to degrade in an open-air environment.
The bags require oxygen to degrade, and a little heat and moisture accelerates the process. We've already learned these elements are not present in a landfill environment. Layers of dirt and debris cover the bags so they can not breathe.
Compostable
Made from vegetable starches such as corn, sugarcane and beetroot, these bags require commercial composting.
This seems like a nice alternative but commercial composting is an extensive process. high heat, aeration, nitrogen and water are used to break down the plastic. They literally need to be cooked to perfection.
This is not your typical backyard compost pile and most municipalities do not allow pet waste in their compost facilities.
Flushable
Made from synthetic polymers, these bags dissolve when immersed in water.
Although the EPA lists flushing pet waste as an option, they do not recommend flushing bags. The bags do not break down very fast and can cause strain on your pipes and municipal water treatment facilities.