Short answer
Snow is a jumble of ice grains and air: light bounces off countless surfaces and comes back out almost unchanged, so it looks white. Ice absorbs red slightly more than blue, and the longer light travels through ice before escaping, the more red it loses — so a hole in deep snow, a crevasse or dense, bubble-free glacier ice looks blue.
A snowpack contains millions of ice grains with air between them. Each grain boundary reflects and refracts a little light, and after many such encounters most of the incoming visible light is sent back out of the surface without any particular preference for one wavelength. Clean snow therefore reflects most visible sunlight and looks white. Its whiteness is structural, like foam or clouds: the ice itself is nearly transparent and faintly blue.
Ice shares liquid water's weak vibrational absorption in the red, shifted slightly to lower energy by hydrogen bonding. The absorption per centimetre is tiny, but it accumulates with distance. Light that enters snow and wanders a metre or more before re-emerging has lost noticeably more red than blue. Poke a hole in deep snow and look in, and the light you see has come the long way round, so it glows blue. The same happens in crevasses, snow caves and the walls of igloos.
Glacier ice begins as snow. Years of burial compress it, forcing out the air between grains and eventually squeezing out bubbles. Bubbly ice behaves like snow: lots of scattering surfaces, short paths, white appearance. Dense, bubble-free ice has few scattering surfaces, so light penetrates deep before being scattered back, and the long path strips out red. The intense blue of glacier caves and freshly calved icebergs is this dense old ice; white bands in the same ice mark bubble-rich layers.
On a sunny day, shadows on snow look distinctly blue for a different reason: they are lit only by the blue sky, and snow, being a neutral reflector, shows that sky colour faithfully. Painters noticed this long before the physics was understood. The blueness of a snow shadow is therefore the colour of skylight, while the blueness inside a snow hole is the colour of ice. On an overcast day, when sky and sun are no longer separate light sources, snow shadows lose most of their blue.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
Clean snow reflects most visible sunlight without preference for any wavelength and so appears white; light emerging after travelling a metre or more through snow contains relatively more blue than red.
Source: Science of snow
FactStrong evidence
Glacier ice appears blue when it has become very dense and free of bubbles through years of compression, because it absorbs red light along the long paths light then travels.
Source: Glacier quick facts
FactStrong evidence
Ice's absorption spectrum resembles liquid water's but with its vibrational peaks shifted to lower energy by hydrogen bonding.
Source: Why is water blue?
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.