It is important to distinguish between the different types of biodegradable plastic, as their costs and uses are very different.

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The two main types are oxo-biodegradable and hydro-biodegradable. In both cases degradation begins with a chemical process (oxidation and hydrolysis respectively), followed by a biological process. Both types emit CO2 as they degrade, but hydro-biodegradable can also emit methane. Both types are compostable, but only oxo-biodegradable can be economically recycled.

Hydro-biodegradable is much more expensive than oxo-biodegradable. (compare hydro and oxo)

This degrades by a process of oxo-biodegradation, initiated by an additive which reduces the molecular weight of the material over a pre-determined period.

The plastic does not just fragment, but is consumed by micro-organisms after the additive has reduced the molecular weight to sub 40,000 Daltons, and it is therefore "biodegradable." This process continues until the material has biodegraded to nothing more than CO2, water, humus, and trace elements. Oxo-biodegradable plastics are made from a by-product of oil refining which would otherwise be wasted. Oil is a finite resource, but the by-product is available because the world will need fuel for engines for the foreseeable future.

There is little or no additional cost, as it can be made with the same machinery and workforce as conventional plastic. The time taken to degrade can be 'programmed' to a few months or a few years, and until the plastic degrades it has the same strength and other characteristics as conventional plastic. Products are protected from degradation by antioxidants until ready for use, and storage-life is extended by cool, dark conditions.

If people want to incinerate oxo-biodegradable products with heat recovery, or recycle them, or re-use them, then that can be done. The key point is what happens to the plastic which is not collected, and gets into the environment as litter. Conventional plastic will subsist in the environment for many decades, but oxo-biodegradable will degrade in a short time leaving no harmful residues.