diff --git a/src/refinement/refinement.jl b/src/refinement/refinement.jl
index ae435e481..35cf6de08 100644
--- a/src/refinement/refinement.jl
+++ b/src/refinement/refinement.jl
@@ -1,19 +1,24 @@
 include("refinement_criteria.jl")
 
-struct ParticleRefinement{RC, ELTYPE}
-    refinement_criteria :: RC
-    max_spacing_ratio   :: ELTYPE
-    mass_ref            :: Vector{ELTYPE} # length(mass_ref) == nparticles
+struct ParticleRefinement{SP, RC, ELTYPE}
+    splitting_pattern         :: SP
+    refinement_criteria       :: RC
+    max_spacing_ratio         :: ELTYPE
+    mass_ref                  :: Vector{ELTYPE} # length(mass_ref) == nparticles
+    n_particles_before_resize :: Int
+    n_new_particles           :: Int
 end
 
-function ParticleRefinement(; max_spacing_ratio,
+function ParticleRefinement(; splitting_pattern, max_spacing_ratio,
                             refinement_criteria=SpatialRefinementCriterion())
     mass_ref = Vector{eltype(max_spacing_ratio)}()
 
     if refinement_criteria isa Tuple
         refinement_criteria = (refinement_criteria,)
     end
-    return ParticleRefinement(refinement_criteria, max_spacing_ratio, mass_ref)
+
+    return ParticleRefinement(splitting_pattern, refinement_criteria, max_spacing_ratio,
+                              mass_ref, 0, 0)
 end
 
 resize_refinement!(system) = system
@@ -37,6 +42,7 @@ function refinement!(semi, v_ode, u_ode, v_tmp, u_tmp, t)
     update_particle_spacing(semi, u_ode)
 
     # Split the particles (Algorithm 2)
+    split_particles!(semi, v_ode, u_ode, v_tmp, u_tmp)
 
     # Merge the particles (Algorithm 3)
 
diff --git a/src/refinement/split.jl b/src/refinement/split.jl
new file mode 100644
index 000000000..a04000b4e
--- /dev/null
+++ b/src/refinement/split.jl
@@ -0,0 +1,103 @@
+function split_particles!(semi, v_ode, u_ode, v_ode_tmp, u_ode_tmp)
+    foreach_system(semi) do system
+        v = wrap_v(v_ode, system, semi)
+        u = wrap_u(u_ode, system, semi)
+        collect_split_candidates!(system, v, u)
+    end
+
+    resize!(semi, v_ode, u_ode, v_ode_tmp, u_ode_tmp)
+
+    foreach_system(semi) do system
+        v = wrap_v(v_ode, system, semi)
+        u = wrap_u(u_ode, system, semi)
+        split_particles!(system, v, u)
+    end
+
+    return semi
+end
+
+@inline collect_split_candidates!(system, v, u) = System
+
+@inline function collect_split_candidates!(system::FluidSystem, v, u)
+    return collect_split_candidates!(system, system.particle_refinement, v, u)
+end
+
+@inline collect_split_candidates!(system::FluidSystem, ::Nothing, v, u) = system
+
+@inline function collect_split_candidates!(system::FluidSystem, particle_refinement, v, u)
+    (; mass_ref, max_spacing_ratio, refinement_pattern) = particle_refinement
+
+    n_split_candidates = 0
+
+    for particle in eachparticle(system)
+        m_a = hydrodynamic_mass(system, particle)
+        m_max = max_spacing_ratio * mass_ref[particle]
+
+        if m_a > m_max
+            n_split_candidates += 1
+        end
+    end
+
+    n_childs_exclude_center = nchilds(system, refinement_pattern) - 1
+
+    particle_refinement.n_new_particles[] = n_split_candidates * n_childs_exclude_center
+
+    return system
+end
+
+@inline split_particles!(system, v, u) = System
+
+@inline function split_particles!(system::FluidSystem, v, u)
+    return split_particles!(system, system.particle_refinement, v, u)
+end
+
+@inline split_particles!(system::FluidSystem, ::Nothing, v, u) = system
+
+@inline function split_particles!(system::FluidSystem, particle_refinement, v, u)
+    (; smoothing_length) = system.cache
+    (; mass_ref, max_spacing_ratio, refinement_pattern, n_particles_before_resize) = particle_refinement
+    (; alpha, relative_position) = refinement_pattern
+
+    for particle in eachparticle(system)
+        m_a = hydrodynamic_mass(system, particle)
+        m_max = max_spacing_ratio * mass_ref[particle]
+
+        if m_a > m_max
+            smoothing_length_old = smoothing_length[particle]
+            mass_old = system.mass[particle]
+
+            system.mass[particle] = mass_old / nchilds(system, refinement_pattern)
+
+            set_particle_pressure!(v, system, partice, pressure)
+
+            set_particle_density!(v, system, partice, density)
+
+            smoothing_length[particle] = alpha * smoothing_length_old
+
+            pos_center = current_coords(system, u, particle)
+            vel_center = current_velocity(system, v, particle)
+
+            for child_id_local in 1:(nchilds(system, refinement_pattern) - 1)
+                child = n_particles_before_resize + child_id_local
+
+                system.mass[child] = mass_old / nchilds(system, refinement_pattern)
+
+                set_particle_pressure!(v, system, child, pressure)
+
+                set_particle_density!(v, system, child, density)
+
+                smoothing_length[child] = alpha * smoothing_length_old
+
+                rel_pos = smoothing_length_old * relative_position[child]
+                new_pos = pos_center + rel_pos
+
+                for dim in 1:ndims(system)
+                    u[dim, child] = new_pos[dim]
+                    v[dim, child] = vel_center[dim]
+                end
+            end
+        end
+    end
+
+    return system
+end