diff --git a/CHANGELOG.md b/CHANGELOG.md
index 409fd7f43..be9b64163 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -69,7 +69,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 #### shells.py
 - Fixes to boolean operations. Added some tolerance parameters to some methods. 
-- Shell3D: get_geo_lines (consider edge.inverse in get_edge_index_in_list check)
+- Shell3D: get_geo_lines (consider edge.inverse in get_edge_index_in_list check), is_shell_open
 
 #### surfaces.py 
 - SphericalSurface3D: use circle 3d instead of polygon3D for plotting. 
diff --git a/volmdlr/edges.py b/volmdlr/edges.py
index 2b0a37df2..3b1efa373 100644
--- a/volmdlr/edges.py
+++ b/volmdlr/edges.py
@@ -721,7 +721,7 @@ def get_shared_section(self, other_linesegment, abs_tol: float = 1e-6):
             if self.__class__ == other_linesegment.simplify.__class__:
                 return self.get_shared_section(other_linesegment.simplify)
             return []
-        if not self.direction_vector().is_colinear_to(other_linesegment.direction_vector()) or \
+        if not self.direction_vector().is_colinear_to(other_linesegment.direction_vector(), 1e-5) or \
                 (not any(self.point_belongs(point, abs_tol)
                          for point in [other_linesegment.start, other_linesegment.end]) and
                  not any(other_linesegment.point_belongs(point, abs_tol) for point in [self.start, self.end])):
diff --git a/volmdlr/shells.py b/volmdlr/shells.py
index 38c730aeb..eefa66674 100644
--- a/volmdlr/shells.py
+++ b/volmdlr/shells.py
@@ -244,7 +244,7 @@ def _helper_create_faces_graph(faces, vertices_points=None, verify_connected_com
         face_vertices = {}
 
         for face_index, face in enumerate(faces):
-            face_contour_primitives = face.outer_contour3d.primitives
+            face_contour_primitives = face.outer_contour3d.primitives[:]
             for inner_contour in face.inner_contours3d:
                 face_contour_primitives.extend(inner_contour.primitives)
             for edge in face_contour_primitives:
@@ -987,14 +987,26 @@ def is_shell_open(faces, faces_graph=None):
         if faces_graph is None:
             vertices_points = Shell3D._helper_getter_vertices_points(faces)
             faces_graph = Shell3D._helper_create_faces_graph(faces, vertices_points, False)
+
+        def is_primitive_on_neighbor_face(prim, neighbor_face):
+            """Verifies if primitive is on a neighbor face."""
+            return any(
+                neighbor_face_contour.is_primitive_section_over_wire(prim)
+                for neighbor_face_contour in [neighbor_face.outer_contour3d] + neighbor_face.inner_contours3d
+            )
+
         for n_index in faces_graph.nodes:
             face = faces[n_index]
-            for prim in face.outer_contour3d.primitives:
-                for neihgbor in faces_graph.neighbors(n_index):
-                    if faces[neihgbor].outer_contour3d.is_primitive_section_over_wire(prim):
-                        break
-                else:
-                    return True
+            if any(
+                    not any(
+                        is_primitive_on_neighbor_face(prim, faces[neighbor])
+                        for neighbor in faces_graph.neighbors(n_index)
+                    )
+                    for prim in [prim for contour in [face.outer_contour3d] + face.inner_contours3d
+                                 for prim in contour.primitives]
+            ):
+                return True
+
         return False
 
     @classmethod