diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index dfe7a75d8..b4dbd9634 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -6718,6 +6718,9 @@ def _pashub_secondary_heating_type_code(
 # cylinder is billed ZERO storage loss.
 _PASHUB_CYLINDER_INSULATION_TO_SAP10: Dict[str, int] = {
     "Factory fitted": 1,  # factory-applied foam
+    # Loose jacket → 2 (gov-API coding; Elmhurst "Jacket" sibling). Table 2
+    # Note 1 gives it its own ~2× higher storage-loss factor.
+    "Loose jacket": 2,
 }