diff --git a/openstack/format.py b/openstack/format.py
index 47902ac6..c50771b3 100644
--- a/openstack/format.py
+++ b/openstack/format.py
@@ -10,31 +10,69 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+from datetime import datetime
+import six
 
-class BoolStr(object):
-    """A custom boolean/string hybrid type for resource.props.
+from oslo_utils import timeutils
 
-    Translates a given value to the desired type.
-    """
-    def __init__(self, given):
-        """A boolean parser.
 
-        Interprets the given value as a boolean, ignoring whitespace and case.
-        A TypeError is raised when interpreted as neither True nor False.
-        """
-        expr = str(given).lower()
-        if 'true' == expr:
-            self.parsed = True
-        elif 'false' == expr:
-            self.parsed = False
+class Formatter(object):
+
+    @classmethod
+    def serialize(cls, value):
+        """Return a string representing the formatted value"""
+        raise NotImplementedError
+
+    @classmethod
+    def deserialize(cls, value):
+        """Return a formatted object representing the value"""
+        raise NotImplementedError
+
+
+class ISO8601(Formatter):
+
+    @classmethod
+    def serialize(cls, value):
+        """Convert a datetime to an ISO8601 string"""
+        if isinstance(value, datetime):
+            return value.isoformat()
+        elif isinstance(value, six.string_types):
+            # If we're already given a string, keep it as-is.
+            # This happens when a string comes back in a response body,
+            # as opposed to the datetime case above which happens when
+            # a user is setting a datetime for a request.
+            return value
         else:
-            msg = 'Invalid as boolean: %s' % given
-            raise ValueError(msg)
+            raise ValueError("Unable to serialize ISO8601: %s" % value)
 
-    def __bool__(self):
-        return self.parsed
+    @classmethod
+    def deserialize(cls, value):
+        """Convert an ISO8601 string to a datetime object"""
+        if isinstance(value, six.string_types):
+            return timeutils.parse_isotime(value)
+        else:
+            raise ValueError("Unable to deserialize ISO8601: %s" % value)
 
-    __nonzero__ = __bool__
 
-    def __str__(self):
-        return str(self.parsed)
+class BoolStr(Formatter):
+
+    # The behavior here primarily exists for the deserialize method
+    # to be producing Python booleans.
+
+    @classmethod
+    def deserialize(cls, value):
+        return cls.convert(value)
+
+    @classmethod
+    def serialize(cls, value):
+        return cls.convert(value)
+
+    @classmethod
+    def convert(cls, value):
+        expr = str(value).lower()
+        if "true" == expr:
+            return True
+        elif "false" == expr:
+            return False
+        else:
+            raise ValueError("Unable to convert as boolean: %s" % value)
diff --git a/openstack/metric/v1/resource.py b/openstack/metric/v1/resource.py
index f776abc5..26ba69a2 100644
--- a/openstack/metric/v1/resource.py
+++ b/openstack/metric/v1/resource.py
@@ -9,9 +9,9 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 # License for the specific language governing permissions and limitations
 # under the License.
+from openstack import format
 from openstack.metric import metric_service
 from openstack import resource
-from openstack import resource_types
 
 
 class Generic(resource.Resource):
@@ -38,10 +38,10 @@ class Generic(resource.Resource):
     project_id = resource.prop('project_id')
     #: Timestamp when this resource was started
     started_at = resource.prop('started_at',
-                               type=resource_types.ISO8601Datetime)
+                               type=format.ISO8601)
     #: Timestamp when this resource was ended
     ended_at = resource.prop('ended_at',
-                             type=resource_types.ISO8601Datetime)
+                             type=format.ISO8601)
     #: A dictionary of metrics collected on this resource
     metrics = resource.prop('metrics', type=dict)
 
diff --git a/openstack/resource.py b/openstack/resource.py
index f57fe0be..b3daaaed 100644
--- a/openstack/resource.py
+++ b/openstack/resource.py
@@ -39,6 +39,7 @@ import six
 from six.moves.urllib import parse as url_parse
 
 from openstack import exceptions
+from openstack import format
 from openstack import utils
 
 
@@ -120,11 +121,10 @@ class prop(object):
                     value = self.type({self.type.id_attribute: value})
                 else:
                     value = self.type(value)
+            elif issubclass(self.type, format.Formatter):
+                value = self.type.deserialize(value)
             else:
                 value = self.type(value)
-                attr = getattr(value, 'parsed', None)
-                if attr is not None:
-                    value = attr
 
         return value
 
@@ -136,6 +136,8 @@ class prop(object):
                     value = self.type({self.type.id_attribute: value})
                 else:
                     value = self.type(value)
+            elif issubclass(self.type, format.Formatter):
+                value = self.type.serialize(value)
             else:
                 value = str(self.type(value))  # validate to fail fast
 
diff --git a/openstack/resource_types.py b/openstack/resource_types.py
deleted file mode 100644
index ef99d955..00000000
--- a/openstack/resource_types.py
+++ /dev/null
@@ -1,20 +0,0 @@
-# Licensed under the Apache License, Version 2.0 (the "License"); you may
-# not use this file except in compliance with the License. You may obtain
-# a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-# License for the specific language governing permissions and limitations
-# under the License.
-import datetime
-
-from oslo_utils import timeutils
-
-
-class ISO8601Datetime(datetime.datetime):
-    def __new__(cls, s):
-        if s:
-            return timeutils.parse_isotime(s)
diff --git a/openstack/tests/unit/test_format.py b/openstack/tests/unit/test_format.py
index f9bf7051..1c50b820 100644
--- a/openstack/tests/unit/test_format.py
+++ b/openstack/tests/unit/test_format.py
@@ -9,33 +9,68 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 # License for the specific language governing permissions and limitations
 # under the License.
+
+from datetime import datetime
+from iso8601 import iso8601
 import testtools
 
 from openstack import format
 
 
-class TestFormat(testtools.TestCase):
-    def test_parse_true(self):
-        self.assertTrue(format.BoolStr(True).parsed)
-        self.assertTrue(format.BoolStr('True').parsed)
-        self.assertTrue(format.BoolStr('TRUE').parsed)
-        self.assertTrue(format.BoolStr('true').parsed)
+class TestBoolStrFormatter(testtools.TestCase):
 
-    def test_parse_false(self):
-        self.assertFalse(format.BoolStr(False).parsed)
-        self.assertFalse(format.BoolStr('False').parsed)
-        self.assertFalse(format.BoolStr('FALSE').parsed)
-        self.assertFalse(format.BoolStr('false').parsed)
+    # NOTE: serialize/deserialize go through the same code path
 
-    def test_parse_fails(self):
-        self.assertRaises(ValueError, format.BoolStr, None)
-        self.assertRaises(ValueError, format.BoolStr, '')
-        self.assertRaises(ValueError, format.BoolStr, 'INVALID')
+    def test_format_true(self):
+        self.assertTrue(format.BoolStr.serialize(True))
+        self.assertTrue(format.BoolStr.serialize('True'))
+        self.assertTrue(format.BoolStr.serialize('TRUE'))
+        self.assertTrue(format.BoolStr.serialize('true'))
 
-    def test_to_str_true(self):
-        self.assertEqual('True', str(format.BoolStr(True)))
-        self.assertEqual('True', str(format.BoolStr('True')))
+    def test_format_false(self):
+        self.assertFalse(format.BoolStr.serialize(False))
+        self.assertFalse(format.BoolStr.serialize('False'))
+        self.assertFalse(format.BoolStr.serialize('FALSE'))
+        self.assertFalse(format.BoolStr.serialize('false'))
 
-    def test_to_str_false(self):
-        self.assertEqual('False', str(format.BoolStr('False')))
-        self.assertEqual('False', str(format.BoolStr(False)))
+    def test_format_fails(self):
+        self.assertRaises(ValueError, format.BoolStr.serialize, None)
+        self.assertRaises(ValueError, format.BoolStr.serialize, '')
+        self.assertRaises(ValueError, format.BoolStr.serialize, 'INVALID')
+
+
+class TestISO8601Formatter(testtools.TestCase):
+
+    def test_deserialize(self):
+        self.assertEqual(
+            format.ISO8601.deserialize("2015-06-27T05:09:43"),
+            datetime(2015, 6, 27, 5, 9, 43, tzinfo=iso8601.UTC))
+        self.assertEqual(
+            format.ISO8601.deserialize("2012-03-28T21:31:02Z"),
+            datetime(2012, 3, 28, 21, 31, 2, tzinfo=iso8601.UTC))
+        self.assertEqual(
+            format.ISO8601.deserialize("2013-09-23T13:53:12.774549"),
+            datetime(2013, 9, 23, 13, 53, 12, 774549, tzinfo=iso8601.UTC))
+        self.assertEqual(
+            format.ISO8601.deserialize("2015-08-27T09:49:58-05:00"),
+            datetime(2015, 8, 27, 9, 49, 58,
+                     tzinfo=iso8601.FixedOffset(-5, 0, "-05:00")))
+
+    def test_serialize(self):
+        self.assertEqual(
+            format.ISO8601.serialize(
+                datetime(2015, 6, 27, 5, 9, 43, tzinfo=iso8601.UTC)),
+            "2015-06-27T05:09:43+00:00")
+        self.assertEqual(
+            format.ISO8601.serialize(
+                datetime(2012, 3, 28, 21, 31, 2, tzinfo=iso8601.UTC)),
+            "2012-03-28T21:31:02+00:00")
+        self.assertEqual(
+            format.ISO8601.serialize(
+                datetime(2013, 9, 23, 13, 53, 12, 774549, tzinfo=iso8601.UTC)),
+            "2013-09-23T13:53:12.774549+00:00")
+        self.assertEqual(
+            format.ISO8601.serialize(
+                datetime(2015, 8, 27, 9, 49, 58,
+                         tzinfo=iso8601.FixedOffset(-5, 0, "-05:00"))),
+            "2015-08-27T09:49:58-05:00")
diff --git a/test-requirements.txt b/test-requirements.txt
index 7ebd60b3..8e7a8f72 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -16,3 +16,4 @@ sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2 # BSD
 testrepository>=0.0.18 # Apache-2.0/BSD
 testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=1.4.0 # MIT
+iso8601>=0.1.9 # MIT