Unlike dunes composed of quartz-based sand, gypsum does not readily convert the sun’s energy into heat. As a result, the surface temperature of White Sands doesn’t get as hot as sand on a beach. Walking barefoot on the dunes is comfortable most of the year. Even when the surface of the sand gets too hot, it is cool just below the surface, because the gypsum retains moisture from the playa of the Alkali Flat.