Hythane is a mixture of natural gas and hydrogen, usually 5-7 percent hydrogen by energy. Natural gas is generally about 90+% methane, along with small amounts of ethane, propane, higher hydrocarbons, and "inerts" like carbon dioxide or nitrogen.

Hydrogen and methane are complimentary vehicle fuels in many ways. Methane has a relatively narrow flammability range that limits the fuel efficiency and oxides of nitrogen (NOx) emissions improvements that are possible at lean air/fuel ratios.

The addition of even a small amount of hydrogen, however, extends the lean flammability range significantly. Methane has a slow flame speed, especially in lean air/fuel mixtures, while hydrogen has a flame speed about eight times faster. Methane is a fairly stable molecule that can be difficult to ignite, but hydrogen has an ignition energy requirement about 25 times lower than methane.

Finally, methane can be difficult to completely combust in the engine or catalyze in exhaust after treatment converters. In contrast, hydrogen is a powerful combustion stimulant for accelerating the methane combustion within an engine, and hydrogen is also a powerful reducing agent for efficient catalysis at lower exhaust temperatures.