Lighter than air solid made of kelp

IMAGINE the unbearable lightness of being a solid that weighs less than air. Scientists have produced just such a material - from a substance found in seaweed.

Kelp, the large broad-leaved seaweed, is an unusually versatile plant. It is already used as a fertiliser, a tasty food in its own right and as the source of agar - a thickener for ice cream. Now a group of scientists at the US government's Lawrence Livermore National University in California has found it can process agar to create an incredibly light solid.

The material, called Seagel (Safe Emulsion Agar gel), is so light it would float away were it not held down by the weight of the microscopically small pockets of air it contains. The solid is safe to eat and biodegradable - when burnt it leaves only carbon dioxide and water.

The scientists make the solid by dissolving the agar in water then adding an organic solvent and an emulsifying agent that disperses the agar through the liquid in tiny droplets, today's issue of New Scientist reports.

The mixture sets to form a gel, and is then hardened by freeze-drying. The scientists can vary the characteristics of the solid for different uses, but claim the lightest version they have made is 10 per cent lighter than air. Some varieties are softer than cotton wool, others as hard as wood.

Most are heavier than the prototype. The team hopes these could be used to replace foam-based packaging and insulation materials such as polystyrene.

The material's inventor, Robert L Morrison, developed a similar solid for the Strategic Defense Initiative. He won the US Department of Energy's Excellence in Nuclear Weapons award in 1990, for his trouble, but yesterday said he could give no details on this related material.