You may wonder why a reflective jacket doesn't look particularly reflective by day, but suddenly seems very reflective at night.
That is because reflective material bounces the light back to the source of light. During the day, the source is all over the sky. At night the source will be a flashlight you are holding or a headlight. The light is bounced directly back from the material, and as you are next to the source of the light, you see the reflected light very well. But if you stood to one side of a person with a reflective material on, it would hardly seem bright at all.
It works this way because reflected material is made with tiny glass beads. They are either made into a yarn (thread) or put in a paint or stuck on a sheet of plastic. A typical reflective material used on clothing is made up of 50,000 tiny glass beads in each square inch. Beads are also used in reflective road paint used on highways.