An alternative to air for inflating tyres. Nitrogen molecules are larger than those of oxygen and are therefore less susceptible to osmotic loss through the tyre casing. Tyres consequently stay at the correct pressure for longer. Since Nitrogen is inert, there is also the argument that it can reduce deterioration of the tyre from inside compared to air. It can also assist in maintaining an even temperature. However, these benefits are marginal because air already contains 78% nitrogen.