SPH is short for Smoothed Particle Hydrodynamics, the method used for simulating fluids in Phun. The SPH particles represent the fluid flow, and thus also the fluid density and velocity field. Particles are affected by a pressure force, a viscosity force, and various external forces (gravity and boundary conditions). The pressure force attempts to conserve the fluid volume, but with the size of the timesteps used in Phun, you will notice that Phun fluids are much more compressible than e.g. water is.

This is a list of variables used for SPH in Phun:

Variable name	Variable type	Description	Default(Phun beta 4.22)
SPH.AVG_density	decimal positive value	average density of the water (related to pressure)
SPH.AVG_neighCount	decimal positive value	average number of neighbouring drops of water
SPH.AVG_pressure	decimal positive value	average pressure exerted on the water
SPH.bucketSize	decimal positive value	use when checking SPH neighbourhood. Changing this value should not affect behavior, but may affect performance.	2.0
SPH.density	decimal positive value	the weight of a water droplet.	1.0
SPH.friction	decimal positive value	the amount of friction experienced between two water droplets.	0.01
SPH.hashInfo	function	gives information about the water. Bucket size, number of particles and average bucket size
SPH.influence	decimal positive value	the influcence radius of an SPH particle. A larger value will give a slower, but maybe more stable, simulation.	2.0
SPH.jitter	decimal positive value	adds random movement to the SPH particle. The larger the value, the stronger forces. A value of 0 means no jitter.	0.0
SPH.pressMultiplier	decimal positive value	multiplication factor of pressure forces	1.0
SPH.radius	decimal positive value	the size of a water droplet.	0.05
SPH.restitution	decimal positive value	the amount of bounciness of the water	0.0
SPH.soundSpeed	decimal positive value	the update frequency of the water system	20.0
SPH.specialPressure	true or false	changes to a different pressure averaging formula	true
SPH.surfaceTension	decimal positive value	not used	0.0
SPH.vaporizeTime	decimal positive value	the time that a water droplet can be idle before it disappears.	5.0
SPH.velocitySmoothing	true or false		true
SPH.viscMultiplier	decimal positive value	multiplication factor of viscosity forces	1.0
SPH.viscosity	decimal positive value	the viscosity of the water	0.5