The Strength slider controls the Transparency effect by surface normals. A higher value will give greater transparency.
The NFactor slider controls the Transparency effected by surface normals. This controls the falloff between transparent and opaque parts of the mesh due to normal direction. A setting of 0 means that all parts of the mesh will be transparent, a setting of 1 means that only normals directly facing the viewer will be transparent.
The ByColor slider controls Transparency effect through color intensity. A higher value will give greater transparency.
The CFactor slider is the color intensity factor: Higher values give greater distinction between colors. A setting of 0 gives no distinction between colors and with a ByColor setting of 1 the mesh will be completely transparent. A setting of 4 will give greatest variation with black areas fully transparent and white areas fully opaque.
The Refract slider controls the amount of refraction: A setting of 0 gives no refraction effect, a setting of 1 gives the greatest refraction.
The RFactor slider controls refraction factor: Higher values give a more exaggerated refraction, effectively multiplying the setting of the Refract slider. Set to a high value for a magnifying lens effect.
Reference Guide > Render > BPR Transparency