Color – Specifies the refraction color of the material. Note that the actual refraction color depends on the Reflection Color as well.

Refraction glossiness – Controls the sharpness of refractions. A value of 1.0 creates perfect glass-like refraction; lower values produce blurry or glossy refractions.

Refraction IOR – Index of refraction for the material, which describes the way light bends when crossing the material surface. A value of 1.0 means that the light does not change direction when hitting the material surface.

Affect shadows – This parameter causes the material to cast transparent shadows. This creates a simple caustic effect, dependent on the refraction color and the fog color. Note: For accurate caustic calculations, disable this parameter and instead enable Caustics. Simultaneous usage of both Caustics and Affects Shadows can be used for artistic purposes but does not produce a physically correct result.

Refract Thin Walled – When enabled, the Fog Scattering mode is set to SSS. It simulates thin translucent surfaces such as soap bubbles, leaves, curtains, etc. The SSS Color defines the backside color, while the SSS Amount controls the translucency effect.

Example: Color

This example demonstrates the effect of the Refraction Color parameter when creating glass materials. For the images in this example, the material has a gray Diffuse Color, a white Reflection Color, and the Fresnel reflections option is enabled.

Example: Refraction IOR

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

Translucency type – Selects the algorithm for calculating translucency (also called sub-surface scattering). Note that Refraction must be enabled for this effect to be visible. See the example.

None – When selected, the only available parameters are the Fog Color and Fog Depth. Together with the Refraction color, they determine the attenuation of light as it passes through the material. In this mode, there is no subsurface scattering.
Volumetric (water) model – Works together with the Refraction Color to scatter light inside the object. This is useful for liquids and other highly transparent materials. The Refraction Color and Refraction Glossiness determine, respectively, how much of the interior of the object is visible and how rays interact with the object’s surface.
SSS (wax) model – Works independently of the Refraction Color/Glossiness and is useful for skin, wax, marble, and other relatively opaque materials.

Illumination method – Determines how direct illumination is computed for sub-surface scattering.

Directional – The directional method tends to propagate more light in the direction from which the surface is lit.
Uniform – The uniform method spreads light more uniformly inside the material. Note that it is not supported on V-Ray GPU.

SSS Amount – Blends between full scattering and pure refraction.

Scatter Color – Controls the scattering. This parameter can be mapped with a texture.

Fog color – Controls the absorption of the material. This parameter can be mapped with a texture.

Depth (cm) –  Controls the strength of the fog effect. Higher values reduce the effect of the fog, making the material more transparent. Smaller values increase the fog effect, making the material more opaque.

Fog depth – 

Trace refractions – Enables refractions for the current material.

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 alpha – Allows the user 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. This is the default value.
Color+alpha – This mode 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.

Enable dispersion – Enables the calculation of true light wavelength dispersion. 

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