The UK's Ministry of Defence spin-off company, Qinetiq, has cooked up an interesting idea - a metal wrapping that helps keeps food cold but can also be used in a microwave without sparking and damaging the machine, as ordinary metal foil does.

The secret is to make the wrapping from thin polyester and cover it with tiny squares of aluminium, the Qinetiq patent reveals. The company has found that aluminium squares 300 micrometres wide, and spaced apart by 100-micrometre tracks of clear plastic, make the perfect heatwave-frequency filter.

Microwaves at the standard frequency and wavelength ignore the grid of squares and can cook the food as normal. But normal heat is reflected, to help keep the food cool.

Enough light passes through the polyester for a cook to see through the packaging and stored food will also stay fresh longer because the polyester is air-tight.(Read the full patent here.)

In nature you have seen flowers and leaves that respond to sunlight. Now an MIT engineer and his German colleagues have created plastics that can be deformed and temporarily fixed into a predetermined shape by light. These programmed materials change shape when exposed to light of wavelengths and return to their original shapes when exposed to light of different wavelengths. The discovery, reported in the April 14 2006 issue of Nature, could have applications in medical and engineering fields.

Plastics with shape-memory--ones that change shape in response to a temperature increase--are well known. Langer and Lendlein reported development of biodegradable versions of these materials in the year 2001. Later, the researchers introduced thermoplastic, biodegradable shape-memory polymers. Now instead of heat they have developed polymers where the shape-memory effect is induced with light. Key to the work: "molecular switches," or photosensitive groups that are grafted onto a permanent polymer network. The resulting photosensitive polymer film is then stretched with an external stress and illuminated with ultraviolet light of a certain wavelength. This prompts the molecular switches to cross link, or bind one to another. The result? When the light is switched off and the external stress released, the cross links remain, maintaining an elongated structure. Exposure to light of another wavelength cleaves the new bonds, allowing the material to spring back to its original shape. It is reported that the temporary shapes are "very stable for long times even when heated to 50 degrees C. An article on this appeared in the April 27, 2005 issue of MIT Tech Talk (Volume 49, Number 25).