Because the particles of water are closer together than the particles of air.
Why is iron a better conductor than water?
Because the particles of iron are closer together than the particles of water.
How do we know that water is a poor conductor of heat?
Because water may be made to boil at its surface without melting ice a short distance below the surface.
How do we know that air is a poor conductor of heat?
Because the air at the ceiling of a room may be made very warm without melting ice near the floor.
Why does a linen shirt feel cool?
Because linen is a good conductor, and there is but little air among its fibres.
Why is a cotton shirt warmer than one made of linen?