diff --git a/masque/label.py b/masque/label.py
index 2a2b56d..2dcf6f2 100644
--- a/masque/label.py
+++ b/masque/label.py
@@ -14,15 +14,15 @@ class Label:
     """
     A circle, which has a position and radius.
     """
-
+    __slots__ = ('_offset', '_layer', '_string', 'identifier')
     # [x_offset, y_offset]
-    _offset = numpy.array([0.0, 0.0])   # type: numpy.ndarray
+    _offset: numpy.ndarray
 
-    # Layer (integer >= 0)
-    _layer = 0                          # type: int or Tuple
+    # Layer (integer >= 0) or 2-Tuple of integers
+    _layer: int or Tuple
 
     # Label string
-    _string = None                      # type: str
+    _string: str
 
     # Arbitrary identifier tuple
     identifier: Tuple
diff --git a/masque/pattern.py b/masque/pattern.py
index fb89f26..aa6c459 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -33,10 +33,11 @@ class Pattern:
             may reference the same Pattern object.
     :var name: An identifier for this object. Not necessarily unique.
     """
-    shapes = None               # type: List[Shape]
-    labels = None               # type: List[Labels]
-    subpatterns = None          # type: List[SubPattern or GridRepetition]
-    name = None                 # type: str
+    __slots__ = ('shapes', 'labels', 'subpatterns', 'name')
+    shapes: List[Shape]
+    labels: List[Label]
+    subpatterns: List[SubPattern or GridRepetition]
+    name: str
 
     def __init__(self,
                  shapes: List[Shape]=(),
diff --git a/masque/repetition.py b/masque/repetition.py
index 8618ba6..ccdf529 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -23,19 +23,30 @@ class GridRepetition:
     GridRepetition provides support for efficiently embedding multiple copies of a Pattern
      into another Pattern at regularly-spaced offsets.
     """
+    __slots__ = ('pattern',
+                 '_offset',
+                 '_rotation',
+                 '_dose',
+                 '_scale',
+                 '_mirrored',
+                 '_a_vector',
+                 '_b_vector',
+                 'a_count',
+                 'b_count',
+                 'identifier')
 
-    pattern = None          # type: Pattern
+    pattern: 'Pattern'
 
-    _offset = (0.0, 0.0)    # type: numpy.ndarray
-    _rotation = 0.0         # type: float
-    _dose = 1.0             # type: float
-    _scale = 1.0            # type: float
-    _mirrored = None        # type: List[bool]
+    _offset: numpy.ndarray
+    _rotation: float
+    _dose: float
+    _scale: float
+    _mirrored: List[bool]
 
-    _a_vector = None        # type: numpy.ndarray
-    _b_vector = None        # type: numpy.ndarray or None
-    a_count = None          # type: int
-    b_count = 1             # type: int
+    _a_vector: numpy.ndarray
+    _b_vector: numpy.ndarray or None
+    a_count: int
+    b_count: int
 
     identifier: Tuple
 
diff --git a/masque/shapes/arc.py b/masque/shapes/arc.py
index ee6bf15..b8e8547 100644
--- a/masque/shapes/arc.py
+++ b/masque/shapes/arc.py
@@ -20,15 +20,14 @@ class Arc(Shape):
     The rotation gives the angle from x-axis, counterclockwise, to the first (x) radius.
     The start and stop angle are measured counterclockwise from the first (x) radius.
     """
-
-    _radii = None           # type: numpy.ndarray
-    _angles = None          # type: numpy.ndarray
-    _width = 1.0            # type: float
-    _rotation = 0.0         # type: float
-
-    # Defaults for to_polygons
-    poly_num_points = DEFAULT_POLY_NUM_POINTS   # type: int
-    poly_max_arclen = None                      # type: float
+    __slots__ = ('_radii', '_angles', '_width', '_rotation',
+                 'poly_num_points', 'poly_max_arclen')
+    _radii: numpy.ndarray
+    _angles: numpy.ndarray
+    _width: float
+    _rotation: float
+    poly_num_points: int
+    poly_max_arclen: float
 
     # radius properties
     @property
@@ -148,6 +147,7 @@ class Arc(Shape):
                  mirrored: Tuple[bool] = (False, False),
                  layer: int=0,
                  dose: float=1.0):
+        self.identifier = ()
         self.radii = radii
         self.angles = angles
         self.width = width
diff --git a/masque/shapes/circle.py b/masque/shapes/circle.py
index 785a382..97df5c0 100644
--- a/masque/shapes/circle.py
+++ b/masque/shapes/circle.py
@@ -14,12 +14,10 @@ class Circle(Shape):
     """
     A circle, which has a position and radius.
     """
-
-    _radius = None                              # type: float
-
-    # Defaults for to_polygons
-    poly_num_points = DEFAULT_POLY_NUM_POINTS   # type: int
-    poly_max_arclen = None                      # type: float
+    __slots__ = ('_radius', 'poly_num_points', 'poly_max_arclen')
+    _radius: float
+    poly_num_points: int
+    poly_max_arclen: float
 
     # radius property
     @property
@@ -46,6 +44,7 @@ class Circle(Shape):
                  offset: vector2=(0.0, 0.0),
                  layer: int=0,
                  dose: float=1.0):
+        self.identifier = ()
         self.offset = numpy.array(offset, dtype=float)
         self.layer = layer
         self.dose = dose
diff --git a/masque/shapes/ellipse.py b/masque/shapes/ellipse.py
index 7064bd5..7915007 100644
--- a/masque/shapes/ellipse.py
+++ b/masque/shapes/ellipse.py
@@ -16,13 +16,12 @@ class Ellipse(Shape):
     An ellipse, which has a position, two radii, and a rotation.
     The rotation gives the angle from x-axis, counterclockwise, to the first (x) radius.
     """
-
-    _radii = None       # type: numpy.ndarray
-    _rotation = 0.0     # type: float
-
-    # Defaults for to_polygons
-    poly_num_points = DEFAULT_POLY_NUM_POINTS   # type: int
-    poly_max_arclen = None                      # type: float
+    __slots__ = ('_radii', '_rotation',
+                 'poly_num_points', 'poly_max_arclen')
+    _radii: numpy.ndarray
+    _rotation: float
+    poly_num_points: int
+    poly_max_arclen: float
 
     # radius properties
     @property
@@ -89,6 +88,7 @@ class Ellipse(Shape):
                  mirrored: Tuple[bool] = (False, False),
                  layer: int=0,
                  dose: float=1.0):
+        self.identifier = ()
         self.radii = radii
         self.offset = offset
         self.rotation = rotation
diff --git a/masque/shapes/path.py b/masque/shapes/path.py
index a09bae1..8e3b385 100644
--- a/masque/shapes/path.py
+++ b/masque/shapes/path.py
@@ -19,10 +19,11 @@ class Path(Shape):
 
     A normalized_form(...) is available, but can be quite slow with lots of vertices.
     """
-    _vertices = None        # type: numpy.ndarray
-    _width = None           # type: float
-    _cap = None             # type: Path.Cap
-    _cap_extensions = None  # type: numpy.ndarray or None
+    __slots__ = ('_vertices', '_width', '_cap', '_cap_extensions')
+    _vertices: numpy.ndarray
+    _width: float
+    _cap: 'Path.Cap'
+    _cap_extensions: numpy.ndarray or None
 
     class Cap(Enum):
         Flush = 0       # Path ends at final vertices
@@ -151,6 +152,9 @@ class Path(Shape):
                  layer: int=0,
                  dose: float=1.0,
                  ) -> 'Path':
+        self._cap_extensions = None     # Since .cap setter might access it
+
+        self.identifier = ()
         self.offset = offset
         self.layer = layer
         self.dose = dose
diff --git a/masque/shapes/polygon.py b/masque/shapes/polygon.py
index 403689c..fda6cd7 100644
--- a/masque/shapes/polygon.py
+++ b/masque/shapes/polygon.py
@@ -18,7 +18,8 @@ class Polygon(Shape):
 
     A normalized_form(...) is available, but can be quite slow with lots of vertices.
     """
-    _vertices = None        # type: numpy.ndarray
+    __slots__ = ('_vertices',)
+    _vertices: numpy.ndarray
 
     # vertices property
     @property
@@ -77,6 +78,7 @@ class Polygon(Shape):
                  layer: int=0,
                  dose: float=1.0,
                  ):
+        self.identifier = ()
         self.layer = layer
         self.dose = dose
         self.vertices = vertices
diff --git a/masque/shapes/shape.py b/masque/shapes/shape.py
index 46123a1..4dca5ae 100644
--- a/masque/shapes/shape.py
+++ b/masque/shapes/shape.py
@@ -24,18 +24,13 @@ class Shape(metaclass=ABCMeta):
     """
     Abstract class specifying functions common to all shapes.
     """
+    __slots__ = ('_offset', '_layer', '_dose', 'identifier')
 
-    # [x_offset, y_offset]
-    _offset = numpy.array([0.0, 0.0])   # type: numpy.ndarray
-
-    # Layer (integer >= 0 or tuple)
-    _layer = 0                          # type: int or Tuple
-
-    # Dose
-    _dose = 1.0                         # type: float
-
-    # An arbitrary identifier for the shape, usually not set but used by Pattern.flatten()
-    identifier = ()                     # type: Tuple
+    _offset: numpy.ndarray      # [x_offset, y_offset]
+    _layer: int or Tuple        # Layer (integer >= 0 or tuple)
+    _dose: float                # Dose
+    identifier: Tuple           # An arbitrary identifier for the shape,
+                                #  usually empty but used by Pattern.flatten()
 
     # --- Abstract methods
     @abstractmethod
diff --git a/masque/shapes/text.py b/masque/shapes/text.py
index d265d64..5824a62 100644
--- a/masque/shapes/text.py
+++ b/masque/shapes/text.py
@@ -16,11 +16,16 @@ __author__ = 'Jan Petykiewicz'
 
 
 class Text(Shape):
-    _string = ''        # type: str
-    _height = 1.0       # type: float
-    _rotation = 0.0     # type: float
-    _mirrored = None    # type: List[str]
-    font_path = ''      # type: str
+    """
+    Text (to be printed e.g. as a set of polygons).
+    This is distinct from non-printed Label objects.
+    """
+    __slots__ = ('_string', '_height', '_rotation', '_mirrored', 'font_path')
+    _string: str
+    _height: float
+    _rotation: float
+    _mirrored: List[str]
+    font_path: str
 
     # vertices property
     @property
diff --git a/masque/subpattern.py b/masque/subpattern.py
index c84305c..745184b 100644
--- a/masque/subpattern.py
+++ b/masque/subpattern.py
@@ -21,13 +21,13 @@ class SubPattern:
     SubPattern provides basic support for nesting Pattern objects within each other, by adding
      offset, rotation, scaling, and associated methods.
     """
-
-    pattern = None          # type: Pattern
-    _offset = (0.0, 0.0)    # type: numpy.ndarray
-    _rotation = 0.0         # type: float
-    _dose = 1.0             # type: float
-    _scale = 1.0            # type: float
-    _mirrored = None        # type: List[bool]
+    __slots__ = ('pattern', '_offset', '_rotation', '_dose', '_scale', '_mirrored', 'identifier')
+    pattern: 'Pattern'
+    _offset: numpy.ndarray
+    _rotation: float
+    _dose: float
+    _scale: float
+    _mirrored: List[bool]
     identifier: Tuple
 
     def __init__(self,