We all know that it is confusing to differentiate between compostable & biodegradable so we have done some research and hopefully this should explain it all fully...
Compostable: This term refers to items that microbes can break down at a rate consistent with other compostable materials, with the right level of heat, water and oxygen. An important aspect of being considered compostable is that an item breaks down over a reasonable period of time (a week to several months). When composted, items should leave behind no discernible residue or toxins, and result in a nutritive soil amendment.
Biodegradable: All compostable items are considered biodegradable, but not all biodegradable items are compostable. Biodegradable packaging means it can degrade from the action of naturally occurring microorganisms such as bacteria, fungi and algae. In and of itself, the term biodegradable makes no claims as to the amount of time needed for degradation, or the attributes of the end product. Something can biodegrade, but take years to biodegrade and therefore would not be compostable. Other things can biodegrade, but leave behind high levels of toxins, contaminants and chemicals and are therefore not compostable. Other items might biodegrade but not do so in a compost environment, and are therefore not compostable.
...and Degradable, well that's a whole new thing!