diff --git a/examples/main.cpp b/examples/main.cpp
index 216f538..1a2ad85 100644
--- a/examples/main.cpp
+++ b/examples/main.cpp
@@ -20,7 +20,7 @@ int main() {
   Material uo2(sigma_t, sigma_s, sigma_a, sigma_f, nu_sigma_f, chi, "UO2");
   std::cout << uo2 << std::endl;
 
-  Cell uo2_cell(1.0, &uo2, "UO2");
+  Cell uo2_cell(1.0, uo2, "UO2");
   std::cout << uo2_cell << std::endl;
 
   return 0;
diff --git a/src/demeter/model/cell.cpp b/src/demeter/model/cell.cpp
index 65daad4..dad71dd 100644
--- a/src/demeter/model/cell.cpp
+++ b/src/demeter/model/cell.cpp
@@ -9,7 +9,10 @@ void Cell::check() const {
 std::string Cell::print() const {
   std::ostringstream ss;
   ss << "Cell " << name_ << " has " << radii_.size() << " rings and "
-     << materials_.size() << " materials";
+     << materials_.size() << " materials:\n";
+  for (const auto& m : materials_) {
+    ss << "  * " << m.get().print();
+  }
   return ss.str();
 }
 }  // namespace Demeter
\ No newline at end of file
diff --git a/src/demeter/model/cell.hpp b/src/demeter/model/cell.hpp
index 16fc7c5..baa45c7 100644
--- a/src/demeter/model/cell.hpp
+++ b/src/demeter/model/cell.hpp
@@ -4,6 +4,8 @@
 #include <string>
 #include <string_view>
 #include <memory>
+#include <functional>
+
 #include <Eigen/Core>
 
 #include "demeter/common.hpp"
@@ -13,13 +15,14 @@ namespace Demeter {
 
 class Cell {
  public:
-  Cell(double side, Material* material, std::string_view name = "")
+  Cell(double side, Material& material, std::string_view name = "")
       : side_(side), name_(name) {
     materials_.push_back(material);
   }
 
   Cell(double side, std::vector<double>& radii,
-       std::vector<Material*>& materials, std::string_view name = "")
+       std::vector<std::reference_wrapper<Material>>& materials,
+       std::string_view name = "")
       : side_(side), radii_(radii), materials_(materials), name_(name) {
     check();
   }
@@ -40,7 +43,7 @@ class Cell {
 
   // size_t num_sectors_; //TODO
 
-  std::vector<Material*> materials_;
+  std::vector<std::reference_wrapper<Material>> materials_;
 
   /* A name for the Cell */
   std::string name_;