Liquid propane

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Propane can only be found in its liquid form when under extreme pressure or in temperatures below -44 degrees Fahrenheit (-42 C). When liquid propane reaches a temperature of -45 degrees Fahrenheit (-42.7 C), it boils and turns into a vapor.

Since liquid propane is an extremely cold substance, it can also be dangerous is handled improperly.^[1]

Liquid propane (LP) gas contains more carbon than natural gas and burns nearly three times hotter.^[2]

References

1. http://www.wisegeek.com/what-is-liquid-propane.htm
2. http://www.elitedeals.com/gaslonagasvs.html