diff --git a/README.md b/README.md
index 282f834..ae83ed0 100644
--- a/README.md
+++ b/README.md
@@ -15,3 +15,10 @@ and this should succeed
 python3 -c "import nhf"
 ```
 
+## Testing
+
+Run all tests with
+``` sh
+python3 -m unittest
+```
+
diff --git a/nhf/materials.py b/nhf/materials.py
new file mode 100644
index 0000000..c752cd4
--- /dev/null
+++ b/nhf/materials.py
@@ -0,0 +1,19 @@
+"""
+A catalog of material properties
+"""
+from enum import Enum
+import cadquery as Cq
+
+def _color(name: str, alpha: float) -> Cq.Color:
+    r, g, b, _ = Cq.Color(name).toTuple()
+    return Cq.Color(r, g, b, alpha)
+
+class Material(Enum):
+
+    WOOD_BIRCH = 0.8, _color('bisque', 0.9)
+    PLASTIC_PLA = 0.5, _color('azure3', 0.6)
+    ACRYLIC_BLACK = 0.5, _color('gray50', 0.6)
+
+    def __init__(self, density: float, color: Cq.Color):
+        self.density = density
+        self.color = color