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Color – Refraction color. Note that the actual refraction color depends on the Reflection Color as well. For more information, see the Refraction Color Parameter example below. 

Glossiness – Controls the sharpness of refractions. A value of 1.0 means perfect glass-like refraction; lower values produce blurry or glossy refractions. For more information, see the Refraction Glossiness Parameter example below.

Index of Refraction – Index of refraction for the material, which describes the way light bends when crossing the material surface. A value of 1.0 means the light does not change direction.  For more information, see the Refraction IOR Parameter example below.

Dispersion – Enables the calculation of true light wavelength dispersion.

Abberation – Allows you to increase or decrease the dispersion effect. Lowering it widens the dispersion and vice versa.

Affect Shadows – Causes the material to cast transparent shadows to create a simple caustic effect dependent on the Refraction Color and the Fog Color. For accurate caustic calculations, disable this parameter and instead enable Caustics in the V-Ray Renderer. Simultaneous usage of both Caustics and Affects Shadows can be used for artistic purposes but does not produce a physically correct result.

Thin Walled – (intended for single-surface transparent materials) When enabled and the Translucency Type is set to SSS, it simulates thin translucent surfaces such as soap bubble, leaves, curtains, etc. The SSS Color defines the backside color, while the SSS Amount controls the translucency effect.

Advanced

Trace Refractions – Enables refractions for the current material.

Use Exit Color – Enables the use of Exit Color.

Exit Color – If a ray has reached it's maximum depth this color is returned instead of tracing the ray further.

Max Depth – The number of times a ray can be refracted. Scenes with lots of refractive and reflective surfaces may require higher values to look correct.

Affect Channels – Allows you to specify which channels are going to be affected by the transparency of the material

Color Only – The transparency affects only the RGB channel of the final render.
Color+Alpha – This causes the material to transmit the alpha of the refracted objects, instead of displaying an opaque alpha. 
All Channels – All channels and render elements are affected by the transparency of the material.

Example: The Refraction Color Parameter

This example demonstrates the effect of the Refraction Color parameter to produce glass materials. For the images in this example, the material is with a grey Diffuse Color, white Reflection Color and Fresnel option on.

Example: The Refraction IOR Parameter

This example demonstrates the effect of the Index of Refraction (IOR) parameter. Note how light bends more as the IOR deviates from 1.0. The case when the IOR is 1.0 produces a transparent object. Note however, that in the case of transparent objects, it might be better to assign an opacity map to the material, rather than use refraction.

Example: The Refraction Glossiness Parameter

This example demonstrates the effect of the Refraction Glossiness parameter. Note how lower Refraction Glossiness values blur the refractions and cause the material to appear as frosted glass.