The lightest powder snow is 95% air and just 5% water.

Snow density is measured by the snow-to-liquid ratio, which typically averages 10:1 in most winter storms. However, in exceptionally cold and dry conditions, this ratio can reach 20:1 or even 30:1, meaning 30 inches of snow would melt down to just 1 inch of water. This phenomenon is most common in high-altitude regions like the Rocky Mountains in the United States.The specific crystal structure responsible for this lightness is called a stellar dendrite. These are six-sided, star-shaped crystals with complex, branching arms that physically prevent other crystals from settling closely together. According to the National Center for Atmospheric Research, these crystals form best when temperatures in the clouds range between −12 and −18 degrees Celsius.Because the branches of stellar dendrites are so thin and fragile, they create a high volume of pore space within the snowpack. This trapped air acts as a natural insulator and provides the "frictionless" sensation reported by elite skiers. If the air is too warm, the crystals melt slightly and bond together, creating "heart attack snow"—heavy, wet snow that lacks the 95% air content of true powder.