Environmental conditions impact dramatically on the life-expectancy of plastic objects. Appropriate environmental conditions are therefore vital. What follows is good practice for the majority of plastics. For cellulose acetate, cellulose nitrate, polyvinyl chloride and polyurethane foam please go to Problem plastics.
Plastics should be kept in a dark, cool, dry room. Whether in store or on display the temperature should be restricted to 20° centigrade and relative humidity to 30 to 50%. Sharp fluctuations of heat and RH are especially damaging.
UV should be filtered out from any light to which plastics are exposed. However, even UV-filtered light is bad for plastics, so when stored, plastics must be kept in the dark and, when on display, light should be limited.
Plastic objects should not be on permanent display. The damage is cumulative and dependent on the overall amount of light, whether a short blast of very bright light or a very low light for a long time.
It is for each curator/conservator to decide what is appropriate for any particular object at any particular time. Recommended good practice varies from a maximum of 50 to 150 lux.