diff --git a/packages/flutter_sprites/lib/flutter_sprites.dart b/packages/flutter_sprites/lib/flutter_sprites.dart
index 97b48b3d5d..41f6830113 100644
--- a/packages/flutter_sprites/lib/flutter_sprites.dart
+++ b/packages/flutter_sprites/lib/flutter_sprites.dart
@@ -34,6 +34,7 @@ part 'src/node3d.dart';
 part 'src/node_with_size.dart';
 part 'src/particle_system.dart';
 part 'src/physics_body.dart';
+part 'src/physics_collision_groups.dart';
 part 'src/physics_debug.dart';
 part 'src/physics_group.dart';
 part 'src/physics_joint.dart';
diff --git a/packages/flutter_sprites/lib/src/node.dart b/packages/flutter_sprites/lib/src/node.dart
index a36cc7783f..b49707fed8 100644
--- a/packages/flutter_sprites/lib/src/node.dart
+++ b/packages/flutter_sprites/lib/src/node.dart
@@ -24,6 +24,7 @@ class Node {
   double _rotation = 0.0;
 
   Matrix4 _transformMatrix = new Matrix4.identity();
+  Matrix4 _transformMatrixInverse;
   Matrix4 _transformMatrixNodeToBox;
   Matrix4 _transformMatrixBoxToNode;
 
@@ -246,9 +247,7 @@ class Node {
       return position;
     } else if (physicsParent is PhysicsGroup) {
       // Transform the position
-      Matrix4 inverseTransform = new Matrix4.copy(physicsParent.transformMatrix);
-      inverseTransform.invert();
-      Vector4 parentPos = inverseTransform.transform(new Vector4(position.x, position.y, 0.0, 1.0));
+      Vector4 parentPos = physicsParent._inverseMatrix().transform(new Vector4(position.x, position.y, 0.0, 1.0));
       Point newPos = new Point(parentPos.x, parentPos.y);
       return _positionToPhysics(newPos, physicsParent.parent);
     } else {
@@ -531,6 +530,7 @@ class Node {
   /// changes that affects the matrix.
   void invalidateTransformMatrix() {
     _transformMatrix = null;
+    _transformMatrixInverse = null;
     _invalidateToBoxTransformMatrix();
   }
 
@@ -575,6 +575,14 @@ class Node {
     return _transformMatrixBoxToNode;
   }
 
+  Matrix4 _inverseMatrix() {
+    if (_transformMatrixInverse == null) {
+      _transformMatrixInverse = new Matrix4.copy(transformMatrix);
+      _transformMatrixInverse.invert();
+    }
+    return _transformMatrixInverse;
+  }
+
   /// Converts a point from the coordinate system of the [SpriteBox] to the local coordinate system of the node.
   ///
   /// This method is particularly useful when handling pointer events and need the pointers position in a local
diff --git a/packages/flutter_sprites/lib/src/physics_body.dart b/packages/flutter_sprites/lib/src/physics_body.dart
index 62e5df5400..7d91dda1ea 100644
--- a/packages/flutter_sprites/lib/src/physics_body.dart
+++ b/packages/flutter_sprites/lib/src/physics_body.dart
@@ -22,7 +22,9 @@ class PhysicsBody {
     bool fixedRotation: false,
     bool bullet: false,
     bool active: true,
-    this.gravityScale: 1.0
+    this.gravityScale: 1.0,
+    collisionCategory: "Default",
+    collisionMask: null
   }) {
     this.density = density;
     this.friction = friction;
@@ -38,6 +40,9 @@ class PhysicsBody {
     this.fixedRotation = fixedRotation;
     this.bullet = bullet;
     this.active = active;
+
+    this.collisionCategory = collisionCategory;
+    this.collisionMask = collisionMask;
   }
 
   Vector2 _lastPosition;
@@ -232,6 +237,46 @@ class PhysicsBody {
 
   double gravityScale;
 
+  Object _collisionCategory = null;
+
+  Object get collisionCategory {
+    return _collisionCategory;
+  }
+
+  set collisionCategory(Object collisionCategory) {
+    _collisionCategory = collisionCategory;
+    _updateFilter();
+  }
+
+  List<Object> _collisionMask = null;
+
+  List<Object> get collisionMask => _collisionMask;
+
+  set collisionMask(List<Object> collisionMask) {
+    _collisionMask = collisionMask;
+    _updateFilter();
+  }
+
+  box2d.Filter get _b2Filter {
+    print("_physicsNode: $_physicsNode groups: ${_physicsNode._collisionGroups}");
+    box2d.Filter f = new box2d.Filter();
+    f.categoryBits = _physicsNode._collisionGroups.getBitmaskForKeys([_collisionCategory]);
+    f.maskBits = _physicsNode._collisionGroups.getBitmaskForKeys(_collisionMask);
+
+    print("Filter: $f category: ${f.categoryBits} mask: ${f.maskBits}");
+
+    return f;
+  }
+
+  void _updateFilter() {
+    if (_body != null) {
+      box2d.Filter filter = _b2Filter;
+      for (box2d.Fixture fixture = _body.getFixtureList(); fixture != null; fixture = fixture.getNext()) {
+        fixture.setFilterData(filter);
+      }
+    }
+  }
+
   PhysicsWorld _physicsNode;
   Node _node;
 
@@ -296,6 +341,8 @@ class PhysicsBody {
   void _attach(PhysicsWorld physicsNode, Node node) {
     assert(_attached == false);
 
+    _physicsNode = physicsNode;
+
     // Account for physics groups
     Point positionWorld = node._positionToPhysics(node.position, node.parent);
     double rotationWorld = node._rotationToPhysics(node.rotation, node.parent);
@@ -333,7 +380,6 @@ class PhysicsBody {
 
     _body.userData = this;
 
-    _physicsNode = physicsNode;
     _node = node;
 
     _attached = true;
@@ -353,6 +399,7 @@ class PhysicsBody {
     fixtureDef.restitution = restitution;
     fixtureDef.density = density;
     fixtureDef.isSensor = isSensor;
+    fixtureDef.filter = _b2Filter;
 
     // Get shapes
     List<box2d.Shape> b2Shapes = <box2d.Shape>[];
diff --git a/packages/flutter_sprites/lib/src/physics_collision_groups.dart b/packages/flutter_sprites/lib/src/physics_collision_groups.dart
new file mode 100644
index 0000000000..6c8a633705
--- /dev/null
+++ b/packages/flutter_sprites/lib/src/physics_collision_groups.dart
@@ -0,0 +1,40 @@
+part of flutter_sprites;
+
+class _PhysicsCollisionGroups {
+
+  _PhysicsCollisionGroups() {
+    // Make sure there is a default entry in the groups
+    getBitmaskForKeys(["Default"]);
+  }
+
+  Map<Object,int> keyLookup = {};
+
+  List<Object> getKeysForBitmask(int bitmask) {
+    List<Object> keys = [];
+    keyLookup.forEach((key, value) {
+      if (value & bitmask) {
+        keys.add(key);
+      }
+    });
+    return key;
+  }
+
+  int getBitmaskForKeys(List<Object> keys) {
+    if (keys == null) {
+      return 0xffff;
+    }
+
+    int bitmask = 0;
+
+    for (Object key in keys) {
+      int value = keyLookup[key];
+      if (value == null) {
+        assert(keyLookup.length < 16);
+        value = 1 << keyLookup.length;
+        keyLookup[key] = value;
+      }
+      bitmask |= value;
+    }
+    return bitmask;
+  }
+}
diff --git a/packages/flutter_sprites/lib/src/physics_world.dart b/packages/flutter_sprites/lib/src/physics_world.dart
index 6a792ca4c3..1472488245 100644
--- a/packages/flutter_sprites/lib/src/physics_world.dart
+++ b/packages/flutter_sprites/lib/src/physics_world.dart
@@ -39,6 +39,8 @@ class PhysicsWorld extends Node {
 
   _ContactHandler _contactHandler;
 
+  _PhysicsCollisionGroups _collisionGroups = new _PhysicsCollisionGroups();
+
   List<PhysicsJoint> _joints = <PhysicsJoint>[];
 
   List<box2d.Body> _bodiesScheduledForDestruction = <box2d.Body>[];