Biodegradable plastic will degrade as a result of bacterial activity. In order to also be classified compostable, the degradation must meet certain specified criteria such as rate biodegradation, maximum residue of material left at a specific point in time and a requirement for the material to have no harmful impact on the final compost or the composting process. All compostable plastic is therefore also biodegradable. The most commonly used standards for compostable plastic are the American standard ASTM #D6400-99, the European standard EN-13432 and DIN V-54900.

Degradable plastic includes all classes of degradable plastic including the biodegradable and compostable. However, plastic that is not biodegradable or compostable usually use the label Degradable plastic. Most of the products using the label Degradable plastic, degrade as result of physical and chemical impact (fracture into smaller pieces of plastic). Biological activity is not a significant part of the degradation of these products, or the process is too slow to earn the classification Biodegradable or Compostable (the biological degradation will typically take many years).

degradable plastic , a plastic designed to undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties that may vary as measured by standard test methods appropriate to the plastic and the application in a period of time that determines its classification.

biodegradable plastic , a degradable plastic in which the degradation results from the action of naturally-occurring micro-organisms such as bacteria, fungi and algae.

compostable plastic, a plastic that undergoes degradation by biological processes during composting to carbon dioxide, water, inorganic compounds, and biomass at a rate consistent with other known, compostable materials and leaves no visually distinguishable or toxic residue.

photo degradable plastic , a degradable plastic in which the degradation results from the action of natural daylight.

Biodegradable plastics are plastics that will decompose in natural aerobic (composting) and anaerobic (landfill) environments. Biodegradation of plastics can be achieved by enabling microorganisms in the environment to metabolize the molecular structure of plastic films to produce an inert humus-like material that is less harmful to the environment. They may be composed of either bioplastics, which are plastics whose components are derived from renewable raw materials, or petroleum-based plastics which utilize an additive. The use of bio-active compounds compounded with swelling agents ensures that, when combined with heat and moisture, they expand the plastic's molecular structure and allow the bio-active compounds to metabolize and neutralize the plastic.

Biodegradable plastics typically are produced in two forms: injection molded (solid, 3D shapes), typically in the form of disposable food service items, and films, typically sold as collection bags for leaves and grass trimmings, and agricultural mulch.

Paper or a biodegradable material made from corn starch? This question has replaced the more traditional "Paper or plastic?" at San Francisco supermarkets, and the New York City Council may follow suit. The bill that council speaker Christine C. Quinn is pushing would not go as far as the San Francisco law, which banned plastic bags outright.

But it would impose a new burden on city supermarkets by requiring them to collect, transport, and recycle used bags. The supermarkets will surely pass on the cost of this new requirement to the consumer in the form of higher prices, yet to our knowledge the plastic-bag debate is proceeding in the absence of any serious cost/benefit analysis. The main knock against plastic bags is that they are not biodegradable. But organic alternatives to plastic, while biodegradable in theory, break down very slowly inside airless landfills, where they actually take up more room than plastic materials. Seeing no compelling evidence that the benefits of yet another mandatory recycling program outweigh the costs, our take on this bill is simple: Bag it.

Compostable products,such as compostable resins, have to fulfil 'clear compostability' criteria to meet the American standards ASTM 6400 D99 and ASTM 6868, and European Bioplastics DIN CERTCO standard EN 13432.

A lesser grade is biodegradable. This term is used to describe products that, under certain conditions, degrade into small fragments within typically a couple of years. This can to some extent be achieved by additives in conventional plastics. There exists no certification for biodegradable products.

Starch based compostable materials are more expensive and they form a more milky film, so there is a market tendency to offer lower cost biodegradable products as a good 'intermediate solution' until the cost and clarity of starch based compostable materials becomes more competitive.

PLA resins are also compostable and offer a mid price option for a degradable solution with excellent clarity for film, sheet and injection moulded products.