diff --git a/examples/EAGLE_ICs/EAGLE_100/vrconfig_3dfof_subhalos_SO_hydro.cfg b/examples/EAGLE_ICs/EAGLE_100/vrconfig_3dfof_subhalos_SO_hydro.cfg
index 2c190e870ab5e2c1af92efe7c13ec2df891aa65b..2903ddd7268aaaae5a290cbf33bd0395f9a629b2 100644
--- a/examples/EAGLE_ICs/EAGLE_100/vrconfig_3dfof_subhalos_SO_hydro.cfg
+++ b/examples/EAGLE_ICs/EAGLE_100/vrconfig_3dfof_subhalos_SO_hydro.cfg
@@ -177,12 +177,11 @@ Reference_frame_for_properties=2 #use the minimum potential as reference frame a
 #Extra fields
 ################################
 
-# Also compute the H abundance as well as the HI, HII and H_2 fractions
-Gas_internal_property_names=ElementMassFractions,SpeciesFractions,SpeciesFractions,SpeciesFractions,
-Gas_internal_property_index_in_file=0,0,1,2,
-Gas_internal_property_input_output_unit_conversion_factors=1.0,1.0,1.0,1.0
-Gas_internal_property_calculation_type =averagemassweighted,averagemassweighted,averagemassweighted,averagemassweighted,
-Gas_internal_property_output_units=unitless,unitless,unitless,unitless,
+# Also compute the HI and H_2 masses in apertures
+Gas_internal_property_names=AtomicHydrogenMasses,MolecularHydrogenMasses,
+Gas_internal_property_input_output_unit_conversion_factors=1.0e10,1.0e10,
+Gas_internal_property_calculation_type=aperture_total,aperture_total,
+Gas_internal_property_output_units=solar_mass,solar_mass,
 
 # Collect the BH subgrid masses and compute the max, min, average and total mass in apertures
 BH_internal_property_names=SubgridMasses,SubgridMasses,SubgridMasses,SubgridMasses,
diff --git a/examples/EAGLE_ICs/EAGLE_12/vrconfig_3dfof_subhalos_SO_hydro.cfg b/examples/EAGLE_ICs/EAGLE_12/vrconfig_3dfof_subhalos_SO_hydro.cfg
index 2c190e870ab5e2c1af92efe7c13ec2df891aa65b..2903ddd7268aaaae5a290cbf33bd0395f9a629b2 100644
--- a/examples/EAGLE_ICs/EAGLE_12/vrconfig_3dfof_subhalos_SO_hydro.cfg
+++ b/examples/EAGLE_ICs/EAGLE_12/vrconfig_3dfof_subhalos_SO_hydro.cfg
@@ -177,12 +177,11 @@ Reference_frame_for_properties=2 #use the minimum potential as reference frame a
 #Extra fields
 ################################
 
-# Also compute the H abundance as well as the HI, HII and H_2 fractions
-Gas_internal_property_names=ElementMassFractions,SpeciesFractions,SpeciesFractions,SpeciesFractions,
-Gas_internal_property_index_in_file=0,0,1,2,
-Gas_internal_property_input_output_unit_conversion_factors=1.0,1.0,1.0,1.0
-Gas_internal_property_calculation_type =averagemassweighted,averagemassweighted,averagemassweighted,averagemassweighted,
-Gas_internal_property_output_units=unitless,unitless,unitless,unitless,
+# Also compute the HI and H_2 masses in apertures
+Gas_internal_property_names=AtomicHydrogenMasses,MolecularHydrogenMasses,
+Gas_internal_property_input_output_unit_conversion_factors=1.0e10,1.0e10,
+Gas_internal_property_calculation_type=aperture_total,aperture_total,
+Gas_internal_property_output_units=solar_mass,solar_mass,
 
 # Collect the BH subgrid masses and compute the max, min, average and total mass in apertures
 BH_internal_property_names=SubgridMasses,SubgridMasses,SubgridMasses,SubgridMasses,
diff --git a/examples/EAGLE_ICs/EAGLE_25/vrconfig_3dfof_subhalos_SO_hydro.cfg b/examples/EAGLE_ICs/EAGLE_25/vrconfig_3dfof_subhalos_SO_hydro.cfg
index 2c190e870ab5e2c1af92efe7c13ec2df891aa65b..2903ddd7268aaaae5a290cbf33bd0395f9a629b2 100644
--- a/examples/EAGLE_ICs/EAGLE_25/vrconfig_3dfof_subhalos_SO_hydro.cfg
+++ b/examples/EAGLE_ICs/EAGLE_25/vrconfig_3dfof_subhalos_SO_hydro.cfg
@@ -177,12 +177,11 @@ Reference_frame_for_properties=2 #use the minimum potential as reference frame a
 #Extra fields
 ################################
 
-# Also compute the H abundance as well as the HI, HII and H_2 fractions
-Gas_internal_property_names=ElementMassFractions,SpeciesFractions,SpeciesFractions,SpeciesFractions,
-Gas_internal_property_index_in_file=0,0,1,2,
-Gas_internal_property_input_output_unit_conversion_factors=1.0,1.0,1.0,1.0
-Gas_internal_property_calculation_type =averagemassweighted,averagemassweighted,averagemassweighted,averagemassweighted,
-Gas_internal_property_output_units=unitless,unitless,unitless,unitless,
+# Also compute the HI and H_2 masses in apertures
+Gas_internal_property_names=AtomicHydrogenMasses,MolecularHydrogenMasses,
+Gas_internal_property_input_output_unit_conversion_factors=1.0e10,1.0e10,
+Gas_internal_property_calculation_type=aperture_total,aperture_total,
+Gas_internal_property_output_units=solar_mass,solar_mass,
 
 # Collect the BH subgrid masses and compute the max, min, average and total mass in apertures
 BH_internal_property_names=SubgridMasses,SubgridMasses,SubgridMasses,SubgridMasses,
diff --git a/examples/EAGLE_ICs/EAGLE_25_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg b/examples/EAGLE_ICs/EAGLE_25_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg
index 2c190e870ab5e2c1af92efe7c13ec2df891aa65b..2903ddd7268aaaae5a290cbf33bd0395f9a629b2 100644
--- a/examples/EAGLE_ICs/EAGLE_25_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg
+++ b/examples/EAGLE_ICs/EAGLE_25_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg
@@ -177,12 +177,11 @@ Reference_frame_for_properties=2 #use the minimum potential as reference frame a
 #Extra fields
 ################################
 
-# Also compute the H abundance as well as the HI, HII and H_2 fractions
-Gas_internal_property_names=ElementMassFractions,SpeciesFractions,SpeciesFractions,SpeciesFractions,
-Gas_internal_property_index_in_file=0,0,1,2,
-Gas_internal_property_input_output_unit_conversion_factors=1.0,1.0,1.0,1.0
-Gas_internal_property_calculation_type =averagemassweighted,averagemassweighted,averagemassweighted,averagemassweighted,
-Gas_internal_property_output_units=unitless,unitless,unitless,unitless,
+# Also compute the HI and H_2 masses in apertures
+Gas_internal_property_names=AtomicHydrogenMasses,MolecularHydrogenMasses,
+Gas_internal_property_input_output_unit_conversion_factors=1.0e10,1.0e10,
+Gas_internal_property_calculation_type=aperture_total,aperture_total,
+Gas_internal_property_output_units=solar_mass,solar_mass,
 
 # Collect the BH subgrid masses and compute the max, min, average and total mass in apertures
 BH_internal_property_names=SubgridMasses,SubgridMasses,SubgridMasses,SubgridMasses,
diff --git a/examples/EAGLE_ICs/EAGLE_50/vrconfig_3dfof_subhalos_SO_hydro.cfg b/examples/EAGLE_ICs/EAGLE_50/vrconfig_3dfof_subhalos_SO_hydro.cfg
index 2c190e870ab5e2c1af92efe7c13ec2df891aa65b..2903ddd7268aaaae5a290cbf33bd0395f9a629b2 100644
--- a/examples/EAGLE_ICs/EAGLE_50/vrconfig_3dfof_subhalos_SO_hydro.cfg
+++ b/examples/EAGLE_ICs/EAGLE_50/vrconfig_3dfof_subhalos_SO_hydro.cfg
@@ -177,12 +177,11 @@ Reference_frame_for_properties=2 #use the minimum potential as reference frame a
 #Extra fields
 ################################
 
-# Also compute the H abundance as well as the HI, HII and H_2 fractions
-Gas_internal_property_names=ElementMassFractions,SpeciesFractions,SpeciesFractions,SpeciesFractions,
-Gas_internal_property_index_in_file=0,0,1,2,
-Gas_internal_property_input_output_unit_conversion_factors=1.0,1.0,1.0,1.0
-Gas_internal_property_calculation_type =averagemassweighted,averagemassweighted,averagemassweighted,averagemassweighted,
-Gas_internal_property_output_units=unitless,unitless,unitless,unitless,
+# Also compute the HI and H_2 masses in apertures
+Gas_internal_property_names=AtomicHydrogenMasses,MolecularHydrogenMasses,
+Gas_internal_property_input_output_unit_conversion_factors=1.0e10,1.0e10,
+Gas_internal_property_calculation_type=aperture_total,aperture_total,
+Gas_internal_property_output_units=solar_mass,solar_mass,
 
 # Collect the BH subgrid masses and compute the max, min, average and total mass in apertures
 BH_internal_property_names=SubgridMasses,SubgridMasses,SubgridMasses,SubgridMasses,
diff --git a/examples/EAGLE_ICs/EAGLE_50_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg b/examples/EAGLE_ICs/EAGLE_50_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg
index 2c190e870ab5e2c1af92efe7c13ec2df891aa65b..2903ddd7268aaaae5a290cbf33bd0395f9a629b2 100644
--- a/examples/EAGLE_ICs/EAGLE_50_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg
+++ b/examples/EAGLE_ICs/EAGLE_50_low_res/vrconfig_3dfof_subhalos_SO_hydro.cfg
@@ -177,12 +177,11 @@ Reference_frame_for_properties=2 #use the minimum potential as reference frame a
 #Extra fields
 ################################
 
-# Also compute the H abundance as well as the HI, HII and H_2 fractions
-Gas_internal_property_names=ElementMassFractions,SpeciesFractions,SpeciesFractions,SpeciesFractions,
-Gas_internal_property_index_in_file=0,0,1,2,
-Gas_internal_property_input_output_unit_conversion_factors=1.0,1.0,1.0,1.0
-Gas_internal_property_calculation_type =averagemassweighted,averagemassweighted,averagemassweighted,averagemassweighted,
-Gas_internal_property_output_units=unitless,unitless,unitless,unitless,
+# Also compute the HI and H_2 masses in apertures
+Gas_internal_property_names=AtomicHydrogenMasses,MolecularHydrogenMasses,
+Gas_internal_property_input_output_unit_conversion_factors=1.0e10,1.0e10,
+Gas_internal_property_calculation_type=aperture_total,aperture_total,
+Gas_internal_property_output_units=solar_mass,solar_mass,
 
 # Collect the BH subgrid masses and compute the max, min, average and total mass in apertures
 BH_internal_property_names=SubgridMasses,SubgridMasses,SubgridMasses,SubgridMasses,
diff --git a/examples/EAGLE_ICs/EAGLE_6/vrconfig_3dfof_subhalos_SO_hydro.cfg b/examples/EAGLE_ICs/EAGLE_6/vrconfig_3dfof_subhalos_SO_hydro.cfg
index 2c190e870ab5e2c1af92efe7c13ec2df891aa65b..2903ddd7268aaaae5a290cbf33bd0395f9a629b2 100644
--- a/examples/EAGLE_ICs/EAGLE_6/vrconfig_3dfof_subhalos_SO_hydro.cfg
+++ b/examples/EAGLE_ICs/EAGLE_6/vrconfig_3dfof_subhalos_SO_hydro.cfg
@@ -177,12 +177,11 @@ Reference_frame_for_properties=2 #use the minimum potential as reference frame a
 #Extra fields
 ################################
 
-# Also compute the H abundance as well as the HI, HII and H_2 fractions
-Gas_internal_property_names=ElementMassFractions,SpeciesFractions,SpeciesFractions,SpeciesFractions,
-Gas_internal_property_index_in_file=0,0,1,2,
-Gas_internal_property_input_output_unit_conversion_factors=1.0,1.0,1.0,1.0
-Gas_internal_property_calculation_type =averagemassweighted,averagemassweighted,averagemassweighted,averagemassweighted,
-Gas_internal_property_output_units=unitless,unitless,unitless,unitless,
+# Also compute the HI and H_2 masses in apertures
+Gas_internal_property_names=AtomicHydrogenMasses,MolecularHydrogenMasses,
+Gas_internal_property_input_output_unit_conversion_factors=1.0e10,1.0e10,
+Gas_internal_property_calculation_type=aperture_total,aperture_total,
+Gas_internal_property_output_units=solar_mass,solar_mass,
 
 # Collect the BH subgrid masses and compute the max, min, average and total mass in apertures
 BH_internal_property_names=SubgridMasses,SubgridMasses,SubgridMasses,SubgridMasses,
diff --git a/src/cooling/COLIBRE/cooling_io.h b/src/cooling/COLIBRE/cooling_io.h
index 1bbc9a16db7156253b2a8f998f675c0d767ba96b..13f4dcda93bddbb7fce9d98b2ca3ec9ec95d3304 100644
--- a/src/cooling/COLIBRE/cooling_io.h
+++ b/src/cooling/COLIBRE/cooling_io.h
@@ -114,6 +114,34 @@ INLINE static void convert_part_sub_species_frac(const struct engine* e,
   ret[2] /= sum;
 }
 
+INLINE static void convert_part_HI_mass(const struct engine* e,
+                                        const struct part* p,
+                                        const struct xpart* xp, float* ret) {
+
+  const float X_H =
+      chemistry_get_metal_mass_fraction_for_cooling(p)[chemistry_element_H];
+
+  const float HI_frac = cooling_get_particle_subgrid_HI_fraction(
+      e->internal_units, e->physical_constants, e->cosmology,
+      e->hydro_properties, e->entropy_floor, e->cooling_func, p, xp);
+
+  *ret = hydro_get_mass(p) * X_H * HI_frac;
+}
+
+INLINE static void convert_part_H2_mass(const struct engine* e,
+                                        const struct part* p,
+                                        const struct xpart* xp, float* ret) {
+
+  const float X_H =
+      chemistry_get_metal_mass_fraction_for_cooling(p)[chemistry_element_H];
+
+  const float H2_frac = cooling_get_particle_subgrid_H2_fraction(
+      e->internal_units, e->physical_constants, e->cosmology,
+      e->hydro_properties, e->entropy_floor, e->cooling_func, p, xp);
+
+  *ret = hydro_get_mass(p) * X_H * H2_frac * 2.f;
+}
+
 /**
  * @brief Specifies which particle fields to write to a dataset
  *
@@ -160,7 +188,23 @@ __attribute__((always_inline)) INLINE static int cooling_write_particles(
       "above deltaT of the entropy floor, the normal hydro quantities are "
       "used.");
 
-  return 4;
+  list[4] = io_make_output_field_convert_part(
+      "AtomicHydrogenMasses", FLOAT, 1, UNIT_CONV_MASS, 0.f, parts, xparts,
+      convert_part_HI_mass,
+      "Atomic hydrogen masses containted in the particles. This quantity is "
+      "obtained from the cooling tables and, if the particle is on the entropy "
+      "floor, by extrapolating to the equilibrium curve assuming constant "
+      "pressure.");
+
+  list[5] = io_make_output_field_convert_part(
+      "MolecularHydrogenMasses", FLOAT, 1, UNIT_CONV_MASS, 0.f, parts, xparts,
+      convert_part_H2_mass,
+      "Molecular hydrogen masses containted in the particles. This quantity is "
+      "obtained from the cooling tables and, if the particle is on the entropy "
+      "floor, by extrapolating to the equilibrium curve assuming constant "
+      "pressure.");
+
+  return 6;
 }
 
 #endif /* SWIFT_COOLING_COLIBRE_IO_H */