To this end, consider the black rubbish bag. A simple thing with just one purpose - to contain your rubbish until you can place it into the outside rubbish bin for later collection. But what happens after that? A lot get taken for land fill and are dumped on a tip. In order for the contents of the bag to bio-degrade properly the bag itself has to break down over time, releasing it's contents to the freedom of a new life underground.
Now, why am I talking about this? well I am often away from my flat and when I am here I don't make all that much rubbish. So the bag doesn't fill up all that quickly. But if the bag is left in contact with the liquid results of decaying rubbish then it statrs to disolve leaving the liquid to collect in the plastic bin and to drip out when the bag is finally changed. This liquid is very very yucky! ... and smelly!
Putting the black bag inside another one made it safe for transporting to the nearest bin without a bio-hazard sticker and some disinfection of the kitchen floor and the plastic bin leaves it all nice and pleasant smelling again.
Ah my life is so exciting.