diff --git a/moderngl_window/opengl/types.py b/moderngl_window/opengl/types.py
index cf16d725..ebf91e85 100644
--- a/moderngl_window/opengl/types.py
+++ b/moderngl_window/opengl/types.py
@@ -17,19 +17,23 @@
 from functools import lru_cache
 from typing import List
 
+VALID_DIVISORS = ['v', 'i']
+
 
 class BufferFormat:
 
-    def __init__(self, format_string: str, components: int, bytes_per_component: int):
+    def __init__(self, format_string: str, components: int, bytes_per_component: int, per_instance=False):
         """
         Args:
             format_string (str): moderngl format string
             components (int): components
             byte_size (int): bytes per component
+            per_instance (bool): Instanced attribute
         """
         self.format = format_string
         self.components = components
         self.bytes_per_component = bytes_per_component
+        self.per_instance = per_instance
 
     @property
     def bytes_total(self) -> int:
@@ -41,26 +45,38 @@ def pad_str(self) -> str:
         return "{}x{}".format(self.components, self.bytes_per_component)
 
     def __str__(self) -> str:
-        return "<BufferFormat {} {} {}>".format(self.format, self.components, self.bytes_per_component)
+        return "<BufferFormat {} components={} bytes_per_component={}>".format(
+            self.format, self.components, self.bytes_per_component)
 
     def __repr__(self) -> str:
         return str(self)
 
 
-@lru_cache(maxsize=200)
-def attribute_format(fmt: str) -> BufferFormat:
+@lru_cache(maxsize=500)
+def attribute_format(attr_format: str) -> BufferFormat:
     """Look up info about an attribute format.
 
     Translate the format into a BufferFormat instance
     containing things like byte size and components
 
     Args:
-        frmt (str): Format of an attribute
+        buffer_format (str): Format of an attribute
     Returns:
         BufferFormat instance
     """
-    if not fmt:
-        raise ValueError("Cannot resolve buffer format: '{}'".format(fmt))
+    if not attr_format:
+        raise ValueError("Cannot resolve buffer format: '{}'".format(attr_format))
+
+    parts = attr_format.split('/')
+
+    # Parse out divisor if present
+    # Examples: 3f/i, 3f/v
+    fmt = parts[0]
+    divisor = ''
+    if len(parts) > 1:
+        divisor = parts[1]
+        if divisor not in VALID_DIVISORS:
+            raise ValueError("Invalid attribute divisor '{}' in '{}'".format(divisor, buffer_format))
 
     # Parse out out component count and actual format
     parts = re.split(r'([fiud])', fmt)
@@ -71,11 +87,14 @@ def attribute_format(fmt: str) -> BufferFormat:
     else:
         bformat = fmt
 
+    # Construct specific buffer format
     fmt_info = buffer_format(bformat)
+    per_instance = divisor == 'i'
     return BufferFormat(
-        '{}{}'.format(components, bformat),
+        '{}{}{}'.format(components, bformat, "/i" if per_instance else ''),
         components,
         fmt_info.bytes_per_component,
+        per_instance=per_instance,
     )
 
 
diff --git a/moderngl_window/opengl/vao.py b/moderngl_window/opengl/vao.py
index 529481ad..069d2e7b 100644
--- a/moderngl_window/opengl/vao.py
+++ b/moderngl_window/opengl/vao.py
@@ -176,7 +176,7 @@ def transform(self, program: moderngl.Program, buffer: moderngl.Buffer,
 
         vao.transform(buffer, mode=mode, vertices=vertices, first=first, instances=instances)
 
-    def buffer(self, buffer, buffer_format: str, attribute_names, per_instance=False):
+    def buffer(self, buffer, buffer_format: str, attribute_names: List[str]):
         """
         Register a buffer/vbo for the VAO. This can be called multiple times.
         adding multiple buffers (interleaved or not)
@@ -185,8 +185,6 @@ def buffer(self, buffer, buffer_format: str, attribute_names, per_instance=False
             buffer: The buffer data. Can be ``numpy.array``, ``moderngl.Buffer`` or ``bytes``.
             buffer_format (str): The format of the buffer. (eg. ``3f 3f`` for interleaved positions and normals).
             attribute_names: A list of attribute names this buffer should map to.
-        Keyword Args:
-            per_instance (bool): Is this buffer per instance data for instanced rendering?
         Returns:
             The ``moderngl.Buffer`` instance object. This is handy when providing ``bytes`` and ``numpy.array``.
         """
@@ -211,7 +209,7 @@ def buffer(self, buffer, buffer_format: str, attribute_names, per_instance=False
         if len(formats) != len(attribute_names):
             raise VAOError("Format '{}' does not describe attributes {}".format(buffer_format, attribute_names))
 
-        self._buffers.append(BufferInfo(buffer, buffer_format, attribute_names, per_instance=per_instance))
+        self._buffers.append(BufferInfo(buffer, buffer_format, attribute_names))
         self.vertex_count = self._buffers[-1].vertices
 
         return buffer