• Use as little material as possible.  This does not mean that you should reduce all wall thicknesses to extremes or design ridiculously tiny components, but the correct and intelligent use of thin wall sections, suitably stiffened with ribs and gussets, will be economically viable.  This philosophy can result in more economic tooling and machinery, and less usage of power.  It also implies that you should choose the best material for the job.  And it implies that you should consider the best methods of assembly, for example the use of snap fitting components will reduce or eliminate the need for bolts or screw fittings.
• Design with recycling in mind.  This can affect your manufacturing plant, not only during normal production runs but also during tool tryout, prototype and pre-production stages, reducing the need for disposal of scrap.  And it can also affect your customers in their future purchases and planning.
• Consider how customer will dispose your products.  Of course, there are long and short term factors.  The intended life of your design or component may be a matter of weeks or may be measured in tens of years.  Many of us have items, such as an old camera, tucked away at the back of a cupboard and rarely used.  Let us consider the future effects on the environment - it need not impose a constraint on your design.

With these guidelines, let consider designing with below conditions:

• Minimise the number of different types of plastic in the component, aiding recycling.
• Reduce the combination of plastic and paint or decorative stripes and finishes.  This also aids recycling and disposal.
• Allow easy disassembly or replacement of the component.
• Minimise the number of separate pieces in any assembly or sub-assembly.
• Optimise wall thickness to reduce material usage, while still meeting the key specification or primary functions.
• Identify the various types of plastic in an assembly by labelling or moulding in identification.
• Minimise the number of non plastic inserts.
• Allow a part to be able to carry out more than one function.

Some of these requirements make good design sense in any case but some are overlooked at times, with consequent wastage in power, material and finance.