diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index 037bf833a..74d08e4cb 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -6260,7 +6260,9 @@ def _map_sap_heating(
             if cylinder_present
             else None
         ),
-        cylinder_insulation_type=heating.water_heating.insulation_type,
+        cylinder_insulation_type=_pashub_cylinder_insulation_type_code(
+            heating.water_heating.insulation_type, cylinder_present
+        ),
         cylinder_insulation_thickness_mm=heating.water_heating.insulation_thickness_mm,
         water_heating_code=water_heating_code,
         water_heating_fuel=water_heating_fuel,
@@ -6370,6 +6372,31 @@ def _pashub_cylinder_size_code(
     return code
 
 
+# PasHub surveyed §Water-Heating cylinder "Insulation Type:" label → SAP10
+# `cylinder_insulation_type` cascade code (foam=1 / jacket=2, mirroring
+# `_ELMHURST_CYLINDER_INSULATION_LABEL_TO_SAP10`). Passed through raw, the
+# storage-loss resolver's `_int_or_none` yields None and a real lodged
+# cylinder is billed ZERO storage loss.
+_PASHUB_CYLINDER_INSULATION_TO_SAP10: Dict[str, int] = {
+    "Factory fitted": 1,  # factory-applied foam
+}
+
+
+def _pashub_cylinder_insulation_type_code(
+    insulation_label: Optional[str], cylinder_present: bool
+) -> Optional[int]:
+    """Resolve a PasHub surveyed cylinder insulation label to the SAP10 code
+    at the mapper boundary (ADR-0015). Returns None when no cylinder is
+    present or the label is genuinely absent; any uncovered non-empty label
+    strict-raises (mirroring `_pashub_cylinder_size_code`)."""
+    if not cylinder_present or not insulation_label:
+        return None
+    code = _PASHUB_CYLINDER_INSULATION_TO_SAP10.get(insulation_label)
+    if code is None:
+        raise UnmappedPasHubLabel("cylinder insulation", insulation_label)
+    return code
+
+
 def _map_sap_ventilation(ventilation: Ventilation) -> SapVentilation:
     return SapVentilation(
         ventilation_type=ventilation.ventilation_type,