Cardboard fizz in the can

Perhaps now, teenagers will really be able to savour the green revolution. British engineers have developed a "cardboard can" which is able to hold fizzy drinks such as colas and beers without bursting.

The benefits are that instead of using non-renewable plastics, or expensive metals such as aluminium and steel, it is simply made of treated cellulose, like that used for milk cartons, with a very thin internal plastic skin to stop gas permeating through the container.

Tens of millions of drinks bottles and cans are used every year in Britain, but comparatively few are recycled - a major cost to the industry and consumers. The new device could be both eco-friendly and eventually lower the cost of canned drinks.

"The object was to make something like the Tetrapak for milk, but for fizzy drinks," said Richard Freeman, of Scientific Generics in Cambridge, who has been working on the design for 18 months. "Aluminium and steel are recyclable - but you can't grow more. And plastic bottles which use PET [a biodegradable plastic] are derived from oil, which is a strictly limited resource."

The new design, which is being discussed with a number of soft drinks manufacturers and brewers, comes in 500 millilitre "cans". They weigh about 50 grams, twice as much as metal cans.

"But the texture is very nice - it feels like wood, not cold like a can. And because it's effectively paper, you can print almost any design on to it - you're not limited as you are with metals."

Producing prototypes of the can proved difficult. Most modern engineering designs are done by modelling them on a computer. But this was not possible with the cardboard, because too little is known about its properties under stress - a key requirement for computer-aided design.

Instead, the design team had to make various shapes and see how they stood up to the pressure of fizzy drinks - which can reach 70 pounds per square inch, equivalent to almost five times atmospheric pressure.

"We thought we would need rounded ends, but what the experiments showed that was weaker, and that actually a point works best," said Dr Freeman. "It's effectively a cylinder with outward-pointing cones at either end." The side of the packaging is extended so that the cones don't protrude past the outside of the can."