These thermometers are made from glass and consist of a glass bulb that is attached to a tube that is marked with a temperature scale. The liquid in the thermometer is usually alcohol or mercury. When this liquid warms up, the molecules in the liquid move faster and the volume expands. The expansion of the liquid causes it to move up into the bore and indicate the temperature. When the liquid cools, it contracts and moves back into the bulb, indicating a low temperature. 

A liquid-in-glass thermometer with a constriction is used to measure the maximum temperature. These types are thermometers are also used to measure the body temperature of humans. As the temperature increases, the liquid moves up into the bore; however, as the liquid cools, it cannot freely move downward again because of a constriction in the bore. In order to lower the liquid in the bore, it must be reset by applying forces to the thermometer sufficient to push the liquid bask into the bulb.