Carbon nanotubes are rolled up sheets of graphite that can have lengths of about 30-100 nanometers and diameters of about a nanometer. Two years ago it was discovered that carbon nanofibres - which consist of bundles of nanotubes - could absorb hydrogen. The Chinese/US team has now synthesised extra-wide nanotubes that can store 4.2% of their weight as hydrogen gas. Some 80% of the absorbed hydrogen can be released at room temperature, and the rest can be released by heating the fibres. Moreover, the nanotubes can be "refuelled" in less than 60 minutes. Carbon nanofibres are also extremely strong, which decreases the chance of an accidental release of the gas and increases their attractiveness to car makers.