diff --git a/ProcessLib/RichardsMechanics/CreateRichardsMechanicsProcess.cpp b/ProcessLib/RichardsMechanics/CreateRichardsMechanicsProcess.cpp
index d901fb3f40a97c73bad8efd10a0ed9caff65e009..7234773c662a7cf2d2fd12961b59f70fc032d59a 100644
--- a/ProcessLib/RichardsMechanics/CreateRichardsMechanicsProcess.cpp
+++ b/ProcessLib/RichardsMechanics/CreateRichardsMechanicsProcess.cpp
@@ -101,9 +101,8 @@ std::unique_ptr<Process> createRichardsMechanicsProcess(
             variable_p->getNumberOfComponents());
     }
 
-    // Constitutive relation.
-    auto solid_material =
-        MaterialLib::Solids::createConstitutiveRelation<DisplacementDim>(
+    auto solid_constitutive_relations =
+        MaterialLib::Solids::createConstitutiveRelations<DisplacementDim>(
             parameters, config);
 
     // Intrinsic permeability
@@ -174,14 +173,15 @@ std::unique_ptr<Process> createRichardsMechanicsProcess(
         //! \ogs_file_param{prj__processes__process__RICHARDS_MECHANICS__material_property}
         config.getConfigSubtree("material_property");
 
-    boost::optional<MeshLib::PropertyVector<int> const&> material_ids;
-    if (mesh.getProperties().existsPropertyVector<int>("MaterialIDs"))
+    auto const material_ids =
+        mesh.getProperties().existsPropertyVector<int>("MaterialIDs")
+            ? mesh.getProperties().getPropertyVector<int>("MaterialIDs")
+            : nullptr;
+    if (material_ids != nullptr)
     {
         INFO(
             "MaterialIDs vector found; the Richards flow is in heterogeneous "
             "porous media.");
-        material_ids =
-            *mesh.getProperties().getPropertyVector<int>("MaterialIDs");
     }
     else
     {
@@ -194,8 +194,9 @@ std::unique_ptr<Process> createRichardsMechanicsProcess(
             flow_material_config, material_ids, parameters);
 
     RichardsMechanicsProcessData<DisplacementDim> process_data{
+        material_ids,
         std::move(flow_material),
-        std::move(solid_material),
+        std::move(solid_constitutive_relations),
         intrinsic_permeability,
         fluid_bulk_modulus,
         biot_coefficient,
diff --git a/ProcessLib/RichardsMechanics/RichardsMechanicsFEM-impl.h b/ProcessLib/RichardsMechanics/RichardsMechanicsFEM-impl.h
index 5d6f227360b9d98cca813a76856fe7e92175ee9f..ae37ff019a5548b11a47cdb0ab494750570b433e 100644
--- a/ProcessLib/RichardsMechanics/RichardsMechanicsFEM-impl.h
+++ b/ProcessLib/RichardsMechanics/RichardsMechanicsFEM-impl.h
@@ -54,10 +54,12 @@ RichardsMechanicsLocalAssembler<ShapeFunctionDisplacement,
                           IntegrationMethod, DisplacementDim>(
             e, is_axially_symmetric, _integration_method);
 
+    auto const material_id = _process_data.material_ids == nullptr
+                                 ? 0
+                                 : (*_process_data.material_ids)[e.getID()];
     for (unsigned ip = 0; ip < n_integration_points; ip++)
     {
-        // displacement (subscript u)
-        _ip_data.emplace_back(*_process_data.solid_material);
+        _ip_data.emplace_back(*_process_data.solid_materials[material_id]);
         auto& ip_data = _ip_data[ip];
         auto const& sm_u = shape_matrices_u[ip];
         _ip_data[ip].integration_weight =
diff --git a/ProcessLib/RichardsMechanics/RichardsMechanicsProcessData.h b/ProcessLib/RichardsMechanics/RichardsMechanicsProcessData.h
index df5a6edf8d02bc2ef5e3bca2b89d08ca5ea9a624..f737f7ce28ada2b4bbc29dcfc7e26832ddf99a16 100644
--- a/ProcessLib/RichardsMechanics/RichardsMechanicsProcessData.h
+++ b/ProcessLib/RichardsMechanics/RichardsMechanicsProcessData.h
@@ -34,11 +34,14 @@ template <int DisplacementDim>
 struct RichardsMechanicsProcessData
 {
     RichardsMechanicsProcessData(
+        MeshLib::PropertyVector<int> const* const material_ids_,
         std::unique_ptr<
             ProcessLib::RichardsFlow::RichardsFlowMaterialProperties>&&
             flow_material_,
-        std::unique_ptr<MaterialLib::Solids::MechanicsBase<DisplacementDim>>&&
-            solid_material_,
+        std::map<int,
+                 std::unique_ptr<
+                     MaterialLib::Solids::MechanicsBase<DisplacementDim>>>&&
+            solid_materials_,
         Parameter<double> const& intrinsic_permeability_,
         Parameter<double> const& fluid_bulk_modulus_,
         Parameter<double> const& biot_coefficient_,
@@ -47,8 +50,9 @@ struct RichardsMechanicsProcessData
         Parameter<double> const& temperature_,
         Eigen::Matrix<double, DisplacementDim, 1>
             specific_body_force_)
-        : flow_material{std::move(flow_material_)},
-          solid_material{std::move(solid_material_)},
+        : material_ids(material_ids_),
+          flow_material{std::move(flow_material_)},
+          solid_materials{std::move(solid_materials_)},
           intrinsic_permeability(intrinsic_permeability_),
           fluid_bulk_modulus(fluid_bulk_modulus_),
           biot_coefficient(biot_coefficient_),
@@ -69,12 +73,16 @@ struct RichardsMechanicsProcessData
     void operator=(RichardsMechanicsProcessData const&) = delete;
     void operator=(RichardsMechanicsProcessData&&) = delete;
 
+    MeshLib::PropertyVector<int> const* const material_ids;
+
     std::unique_ptr<ProcessLib::RichardsFlow::RichardsFlowMaterialProperties>
         flow_material;
 
     /// The constitutive relation for the mechanical part.
-    std::unique_ptr<MaterialLib::Solids::MechanicsBase<DisplacementDim>>
-        solid_material;
+    std::map<
+        int,
+        std::unique_ptr<MaterialLib::Solids::MechanicsBase<DisplacementDim>>>
+        solid_materials;
     /// Permeability of the solid. A scalar quantity, Parameter<double>.
     Parameter<double> const& intrinsic_permeability;
     /// Fluid's bulk modulus. A scalar quantity, Parameter<double>.