diff --git a/wafo/sg_filter/__init__.py b/wafo/sg_filter/__init__.py
new file mode 100644
index 0000000..40c606d
--- /dev/null
+++ b/wafo/sg_filter/__init__.py
@@ -0,0 +1,2 @@
+from wafo.sg_filter._core import *
+from wafo.sg_filter import demos
diff --git a/wafo/sg_filter.py b/wafo/sg_filter/_core.py
similarity index 100%
rename from wafo/sg_filter.py
rename to wafo/sg_filter/_core.py
diff --git a/wafo/demo_sg.py b/wafo/sg_filter/demos.py
similarity index 100%
rename from wafo/demo_sg.py
rename to wafo/sg_filter/demos.py
diff --git a/wafo/sg_filter/tests/__init__.py b/wafo/sg_filter/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/wafo/sg_filter/tests/conftest.py b/wafo/sg_filter/tests/conftest.py
new file mode 100644
index 0000000..5c8859b
--- /dev/null
+++ b/wafo/sg_filter/tests/conftest.py
@@ -0,0 +1,12 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+"""
+    Dummy conftest.py for wafo.
+
+    If you don't know what this is for, just leave it empty.
+    Read more about conftest.py under:
+    https://pytest.org/latest/plugins.html
+"""
+from __future__ import print_function, absolute_import, division
+
+import pytest  # @UnusedImport
diff --git a/wafo/tests/test_sg_filter.py b/wafo/sg_filter/tests/test_sg_filter.py
similarity index 100%
rename from wafo/tests/test_sg_filter.py
rename to wafo/sg_filter/tests/test_sg_filter.py