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Bubbles – Each particle is shaded as a spherical, transparent, reflective foam bubble. Surfaces of bubbles that intersect one another are visible inside the bubbles. If you get flickering or noisy renders of tightly packed masses of foam such as beer heads, you should switch to Cellular mode. Otherwise, in animation, pairs of bubbles would appear with one bubble completely in front of another in one frame, and completely behind on the next frame, once the bubble's center goes behind the other bubble's center. This would cause abrupt changes in the overall look of the foam mass in animation.
Cellular – Similar to Bubble mode, but replaces intersecting walls between bubbles with a curved wall. The degree of curvature is determined by the Pressure variation parameter. This mode is about twice as slow as simple Bubbles but is suitable for close-up foam. 
Splashes – Each particle is shaded as a spherical, opaque, reflective droplet. Surfaces of droplets that intersect one another are not visible.
Points – Particles are shaded as flat discs, each the size of one pixel by default. This mode is faster than Bubbles, Cellular, and Splashes and thus is suitable for large scale foam and splashes over a large surface, such as an ocean surface. This mode is also suitable for rendering non-foamy fluids such as smoke or ink.
Fog – Each particle is put into a grid and the smoke shader is used to visualize the grid's content. This mode is an alternative to Point mode.

Subgroup | subgroup – Selectively shades particles, depending on their position relative to the liquid surface. See the Liquid Simulator parameter below.–  The Particle Shader can skip rendering some particles depending on the selected condition:

All – All – All the particles are shadedrendered.
Under Water –  – Only particles inside the mesh volume of the connected connected Liquid Simulator are  are shaded. Note that when when Mode is  is set to to Splashes, particles will not render with the the Under Water subgroup  subgroup as it would produce no effect to render liquid drops submerged in the liquid surface. This is because splash particles would die when they merge back into the liquid volume - see FLIP Particles Life Cycle.
Above Water –  – Only particles outside the mesh volume of the connected Liquid Simulator are  are shaded.
Below Size Threshold –  – Only particles smaller than the the Size limitThreshold value are rendered.
Above Size Threshold –  – Only particles larger than the the Size limit value Threshold value are rendered.

Color | color – Specifies the particle color.

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Size Threshold | sizelimit – If the particle count is very high and most particles are indiscernible from the camera position, using separate shading techniques for large and small particles will give better results. This parameter works in combination with the Subgroup parameter for this purpose. When the Subgroup parameter is set to Above the size limit or Below the size limitSize Threshold or Below Size Threshold, the shader only renders particles that satisfy the condition. Use a second Particle Shader object to render the rest of the particles by setting the opposite condition. This makes it possible to have different shading for big and small bubbles or droplets.

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