Propane is affected by temperature change, as is most everything on the planet. Like the human body, propane reacts to temperature change. When it is cold, it becomes denser and, when it is warm, it expands. This means that in terms of a closed tank of propane, the level of propane will vary depending on the outside temperature. Yet, the quantity of energy is constant. However, it is indicated that the propane liquid is denser. Nevertheless, the energy remains the same and the mass, i.e. the weight, also.