MIDEL eN 1215 and MIDEL eN 1204 Natural Ester Materials Compatibility

As a general rule, materials that are used in the manufacture of standard mineral oil-filled transformers are compatible with MIDEL eN 1215 and MIDEL eN 1204 (natural ester fluids).

These lists of compatible and incompatible materials have been compiled through a combination of testing and read across to external data related to vegetable oils. In all cases the user should confirm the suitability of any material to be used in equipment with MIDEL ester-based liquids.

It also draws attention to materials which are considered incompatible or are recommended for use only in particular circumstances. For example neoprene rubber may be used as a binder in cork composites but should not be used on its own. The list is not exhaustive and is intended for guidance only.

Materials are listed by type but within a specific type there may be available several proprietary formulations. The response of different formulations to MIDEL ester-based liquids may vary according to the additives used. This applies particularly to elastomers and polymers.

It is strongly recommended that if a material not listed is critical to equipment performance the manufacturer should be consulted and tests carried out. We would be pleased to liaise with the manufacturer and if necessary carry out tests ourselves.

Application Compatible Materials
Seals and ‘O’ Rings Nitrile Rubber (BS2751)1, Fluorocarbon Rubber (Viton), PTFE (Teflon), Nylon, EPR/EPDM, Fluorosilicone
Gaskets and Jointings Cork Bonded with Nitrile / Chloroprene (WCL TD1120),
Wire and Wire Enamels Polyester, Epoxy
Tank Enamels2 Epoxy
Insulating Varnishes Epoxy
Plastics / Sheet boPET (Mylar), Polyester (Melinex), Glass / Epoxy Resin (HGW), Polyetheretherketone (PEEK),  Polypropylene, Fibre Reinforced Epoxy Glass (FRP), Epoxy resin (EPIKOTE, Araldite CY255, EPR681, EPR163, Epotec YDC 6015), Polyurethane resin (BAYGAL), Nylon, PPS
Sleevings Epoxy / Glass,  Polyester / Glass
Metals Copper, Aluminium, Core Steel
Paints Epoxy based (Inver V0098)
Adhesives Casein, Epoxy, Syanoacrylate, PUR resin, PVA resin
Miscellaneous Kraft Paper, Thermally Upgraded Kraft Paper, Aramid Paper (Nomex, Teijin D8335), Pressboard3, Phenolic Paper Laminate, Porcelain, Cotton Tape, Diamond Patterned Epoxy Paper, Plywood
1. Nitrile rubber is produced in many grades, some of which may contain additives or binders which are not compatible with MIDEL eN 1215/1204, For this reason it is recommended that customers use BS2751 Nitrile.
2. Tank Enamels based on natural resins (solvented in IMS), although resistant to MIDEL eN 1204/1215, may leach out acidity on ageing.

3. Certain papers and pressboards may release dye into MIDEL eN 1204/1215. This has not been found to adversely affect MIDEL eN 1204/1215 or its insulation properties.


Application Incompatible Materials
Rubber and Plastics EPDM, Neoprene Rubber, Natural Rubber, Polychloroprene, Polystyrene, Cross Linked Polyethylene (XLPE), Cross Linked Polyolefin (Raychem ZHTM), AQP Elastomer
Hose Cross Linked Polyolefin (Raychem ZHTM), AQP Elastomer (Aeroquip FC332AQP), Elastomer (Raychem DR-25-1-0-SP), UV Stabilised Polyolefin (Raychem HX-SCE)
Sealant Low Modulus Silicone (Bostik Bond-Flex)
Metals Zinc plated steel and Zinc paints
Miscellaneous Ethylene Propylene Rubber (Self Amalgamating Tape)