diff --git a/src/neutronics_material_maker/data/breeder_materials.json b/src/neutronics_material_maker/data/breeder_materials.json
index d67206c..2d9a756 100644
--- a/src/neutronics_material_maker/data/breeder_materials.json
+++ b/src/neutronics_material_maker/data/breeder_materials.json
@@ -1,7 +1,7 @@
 {
     "Li": {
         "chemical_equation": "Li",
-        "density": "0.515 - 1.01e-4 * (temperature + 273.15 - 200)",
+        "density": "0.515 - 1.01e-4 * (temperature - 273.15 - 200)",
         "density_unit": "g/cm3",
         "comment": "http://aries.ucsd.edu/LIB/PROPS/PANOS/li.html",
         "percent_type": "ao",
diff --git a/src/neutronics_material_maker/data/multiplier_and_breeder_materials.json b/src/neutronics_material_maker/data/multiplier_and_breeder_materials.json
index 789d85d..14a2591 100644
--- a/src/neutronics_material_maker/data/multiplier_and_breeder_materials.json
+++ b/src/neutronics_material_maker/data/multiplier_and_breeder_materials.json
@@ -1,7 +1,7 @@
 {
     "Pb842Li158": {
         "chemical_equation": "Pb842Li158",
-        "density": "99.90*(0.1-16.8e-6*(temperature + 273.15))",
+        "density": "99.90*(0.1-16.8e-6*(temperature - 273.15))",
         "density_unit": "g/cm3",
         "comment": "density equation valid for in the range 240-350 C. source http://aries.ucsd.edu/LIB/PROPS/PANOS/lipb.html",
         "percent_type": "ao",
@@ -10,7 +10,7 @@
     },
     "lithium-lead": {
         "chemical_equation": "Pb842Li158",
-        "density": "99.90*(0.1-16.8e-6*(temperature + 273.15))",
+        "density": "99.90*(0.1-16.8e-6*(temperature - 273.15))",
         "density_unit": "g/cm3",
         "comment": "density equation valid for in the range 240-350 C. source http://aries.ucsd.edu/LIB/PROPS/PANOS/lipb.html",
         "percent_type": "ao",
@@ -29,7 +29,7 @@
     },
     "FLiBe": {
         "chemical_equation": "F2Li2BeF2",
-        "density": "2.214 - 4.2e-4 * (temperature + 273.15)",
+        "density": "2.214 - 4.2e-4 * (temperature - 273.15)",
         "density_unit": "g/cm3",
         "comment": "source http://aries.ucsd.edu/LIB/MEETINGS/0103-TRANSMUT/gohar/Gohar-present.pdf",
         "percent_type": "ao",