diff --git a/ProcessLib/TH2M/ConstitutiveRelations/Base.h b/ProcessLib/TH2M/ConstitutiveRelations/Base.h
index d0f26028eca002d68e9daa55417801abd26c1742..a2bcea4a0dcc1887720c3dcd3b4aa661ef9cd662 100644
--- a/ProcessLib/TH2M/ConstitutiveRelations/Base.h
+++ b/ProcessLib/TH2M/ConstitutiveRelations/Base.h
@@ -47,8 +47,8 @@ struct MediaData
 
 struct TemperatureData
 {
-    double T;
-    double T_prev;
+    double T = nan;
+    double T_prev = nan;
 };
 
 using ReferenceTemperatureData =
diff --git a/ProcessLib/TH2M/ConstitutiveRelations/FluidDensity.h b/ProcessLib/TH2M/ConstitutiveRelations/FluidDensity.h
index 067bc887273ab6ca921f99dd99cd6b0fd5e34f12..22a0fa60d878c689c00df93cb86e5899d4535845 100644
--- a/ProcessLib/TH2M/ConstitutiveRelations/FluidDensity.h
+++ b/ProcessLib/TH2M/ConstitutiveRelations/FluidDensity.h
@@ -19,10 +19,10 @@ namespace ConstitutiveRelations
 struct FluidDensityData
 {
     // gas phase density
-    double rho_GR = 0.;
+    double rho_GR = nan;
 
     // liquid phase density
-    double rho_LR = 0.;
+    double rho_LR = nan;
 
     static auto reflect()
     {
diff --git a/ProcessLib/TH2M/ConstitutiveRelations/MassMoleFractions.h b/ProcessLib/TH2M/ConstitutiveRelations/MassMoleFractions.h
index a63b2514a47ef459a9e87268578f30b7e0f2b263..a180d179d839ae450dd80709d71a429947eed351 100644
--- a/ProcessLib/TH2M/ConstitutiveRelations/MassMoleFractions.h
+++ b/ProcessLib/TH2M/ConstitutiveRelations/MassMoleFractions.h
@@ -18,10 +18,10 @@ namespace ConstitutiveRelations
 {
 struct MassMoleFractionsData
 {
-    double xnCG = 0.;
-    double xmCG = 0.;
-    double xnWL = 0.;
-    double xmWL = 0.;
+    double xnCG = nan;
+    double xmCG = nan;
+    double xnWL = nan;
+    double xmWL = nan;
 
     static auto reflect()
     {
diff --git a/ProcessLib/TH2M/ConstitutiveRelations/SolidThermalExpansion.h b/ProcessLib/TH2M/ConstitutiveRelations/SolidThermalExpansion.h
index 9f225f30f7d2691173ea2bdde69fd1f136db19af..3eeab68c3d20889880593388ee6e16a36570aa69 100644
--- a/ProcessLib/TH2M/ConstitutiveRelations/SolidThermalExpansion.h
+++ b/ProcessLib/TH2M/ConstitutiveRelations/SolidThermalExpansion.h
@@ -19,8 +19,8 @@ template <int DisplacementDim>
 struct SolidThermalExpansionData
 {
     KelvinVector<DisplacementDim> solid_linear_thermal_expansivity_vector;
-    double beta_T_SR;  /// Isotropic solid phase volumetric thermal expansion
-                       /// coefficient.
+    double beta_T_SR = nan;  /// Isotropic solid phase volumetric thermal
+                             /// expansion coefficient.
     double thermal_volume_strain = nan;
 };