diff --git a/README.md b/README.md
index a80679f..f3fa8b0 100644
--- a/README.md
+++ b/README.md
@@ -129,6 +129,9 @@ Developers, please make pull requests to the https://github.com/elmbeech/physice
 
 
 ## Release Notes:
++ version 4.1.1 (2026-02-28): elmbeech/physicelldataloader
+    + reduce memory footprint.
+
 + version 4.1.0 (2025-12-31): elmbeech/physicelldataloader
     + new TimeStep class and TimeSeris class function **get_spatialdata** and command line command **pcdl_get_spatialdata**.
 
diff --git a/pcdl/VERSION.py b/pcdl/VERSION.py
index fa721b4..47cbba7 100644
--- a/pcdl/VERSION.py
+++ b/pcdl/VERSION.py
@@ -1 +1 @@
-__version__ = '4.1.0'
+__version__ = '4.1.1'
diff --git a/pcdl/timestep.py b/pcdl/timestep.py
index 05e1a84..97671fd 100644
--- a/pcdl/timestep.py
+++ b/pcdl/timestep.py
@@ -3333,6 +3333,11 @@ def _read_xml(self, xmlfile, output_path='.'):
             except AttributeError:
                 pass
 
+        ###############
+        # free memory #
+        ###############
+        del d_mcds['raw_substrate']
+        del d_mcds['raw_cell']
 
         ##########
         # output #