* Bend light more strongly. The higher the index of refraction, the more the light will bend (or refract) as it passes from one medium to another.

* Slow down light more. Light travels slower in materials with higher indices of refraction.

* Have a greater optical density. Optical density is a measure of how much a material slows down light, and it is directly related to the index of refraction.

Examples of materials with high indices of refraction:

* Diamond: Its high index of refraction (2.42) is what gives it its brilliant sparkle.

* Glass: Typical glass has an index of refraction around 1.5.

* Water: Water has a relatively lower index of refraction (1.33) compared to glass and diamond.

In contrast, materials with low indices of refraction:

* Air: Has an index of refraction close to 1.

* Vacuum: Has an index of refraction of exactly 1.

Let me know if you'd like more information about a specific material or aspect of refraction!