diff --git a/cura/Machines/ContainerGroup.py b/cura/Machines/ContainerGroup.py
index 5c34f0f123..1061abadda 100644
--- a/cura/Machines/ContainerGroup.py
+++ b/cura/Machines/ContainerGroup.py
@@ -1,10 +1,13 @@
+from typing import Optional
+
 from PyQt5.Qt import QObject
 
 from cura.Machines.ContainerNode import ContainerNode
 
 
 class ContainerGroup(QObject):
+
     def __init__(self, parent = None):
         super().__init__(parent)
-        self.node_for_global = None  # type: ContainerNode
+        self.node_for_global = None  # type: Optional[ContainerNode]
         self.nodes_for_extruders = dict()
diff --git a/cura/Machines/ContainerNode.py b/cura/Machines/ContainerNode.py
index b9ebaa698a..059bccba0d 100644
--- a/cura/Machines/ContainerNode.py
+++ b/cura/Machines/ContainerNode.py
@@ -3,25 +3,37 @@ from typing import Optional
 from collections import OrderedDict
 
 from UM.Logger import Logger
+from UM.Settings.InstanceContainer import InstanceContainer
 
 
-##  A metadata / container combination. Use getContainer to get the container corresponding to the metadata
+##
+# A metadata / container combination. Use getContainer() to get the container corresponding to the metadata.
+#
+# ContainerNode is a multi-purpose class. It has two main purposes:
+#  1. It encapsulates an InstanceContainer. It contains that InstanceContainer's
+#          - metadata (Always)
+#          - container (lazy-loaded when needed)
+#  2. It also serves as a node in a hierarchical InstanceContainer lookup table/tree.
+#     This is used in Variant, Material, and Quality Managers.
+#
 class ContainerNode:
-    def __init__(self, metadata = None):
+    __slots__ = ("metadata", "container", "children_map")
+
+    def __init__(self, metadata: Optional[dict] = None):
         self.metadata = metadata
         self.container = None
         self.children_map = OrderedDict()
 
-    def getChildNode(self, child_key: str) -> Optional["QualityNode"]:
+    def getChildNode(self, child_key: str) -> Optional["ContainerNode"]:
         return self.children_map.get(child_key)
 
     def getContainer(self) -> "InstanceContainer":
         if self.metadata is None:
-            raise RuntimeError("Cannot get container for a QualityNode without metadata")
+            raise RuntimeError("Cannot get container for a ContainerNode without metadata")
 
         if self.container is None:
             container_id = self.metadata["id"]
-            Logger.log("d", "Lazy-loading container [%s]", container_id)
+            Logger.log("i", "Lazy-loading container [%s]", container_id)
             from UM.Settings.ContainerRegistry import ContainerRegistry
             container_list = ContainerRegistry.getInstance().findInstanceContainers(id = container_id)
             if not container_list:
@@ -30,5 +42,5 @@ class ContainerNode:
 
         return self.container
 
-    def __str__(self):
+    def __str__(self) -> str:
         return "ContainerNode[%s]" % self.metadata.get("id")