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As mentioned under “Blend factor”, radius represents the size of the metaballs around the particles. With a “Blend factor” of 0.0 each particle is displayed as a sphere with the adjusted radius. Very large “Radius” values normally lead to a roundish mesh with thick borders. A good starting point is the currently adjusted “Polygon size”. In combination with the default “Blend factor” of 95 you often get an already convincing mesh, or at least something you can play and experiment with to get the desired result. “Radius” can be very small, even below 0.01, but there is a limit when no mesh polygons are being created at all. This limit depends on your fluid simulation and number of particles. A “Blend factor” of 0.0 can be used to visualize the individual spheres of a mesh. The parameter's unit is metres [m].
Subtractive field
By default, meshes from multiple emitters are added and blended together, but it is also possible to subtract them. If you want to subtract an emitter from another, simply activate its “Subtractive field” option.
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