HOSTAPHAN is the brand name of the biaxially oriented polyester film (BOPET) made by Mitsubishi Polyester Film GmbH in Wiesbaden, Germany: a film of polyethylene terephthalate that is stretched lengthwise and crosswise and then heat-set. The RN and WN grades in particular are intended for electrical insulation. They run in thermal class B with a continuous rating of 130 °C, have a permittivity of 3.3 and a dissipation factor of 0.002 at 23 °C and 50 Hz (Mitsubishi, General Technical Data 06/2026), and a 50 µm film withstands a breakdown voltage of 12 kV. This article sorts the grades, reads the data sheets and shows how we, as the largest European converter of Mitsubishi Hostaphan in thick films, process the film in our polyester film programme into rolls and stamped parts.
HOSTAPHAN from GOBA: supply forms, thicknesses and enquiry
GOBA supplies HOSTAPHAN from a single piece, as material or as a finished part to your drawing.
- Supply forms
- Roll and slit roll, Sheet and board, Cut-to-size, Die-cut part to drawing, Formed part (folded, embossed or bent)
- Thicknesses
- To your specification. GOBA processes materials from 7 µm to 3 mm.
- Versions
- HOSTAPHAN by Mitsubishi Polyester Film, for example RN and WN, with a focus on thick films. If your drawing specifies HOSTAPHAN, we supply exactly that brand.
- Slit rolls
- Widths from 5 to 1,600 mm, tolerance ±0.1 mm, cores of 25, 55, 76 or 152 mm
- Die-cut and formed parts
- Material thickness 0.023 to 3.0 mm, dimensions up to 1,000 × 2,000 mm
- Quantity
- From 1 piece, from sample to series
- Lead time
- Two weeks at most when the material is in stock
What we need for your quotation
- Drawing or dimensions
- Quantity
- Material and thickness
For rolls also width, length, core diameter, core material (for example plastic) and tolerances.
HOSTAPHAN has come from Wiesbaden since 1957
The brand is older than most of the motors it sits in today. Hoechst acquired the licence for polyester film from ICI in 1953, ran a pilot line with a web width of 0.8 m in Wiesbaden in 1955 and started the first commercial production in 1957. By 1969 a 4 m wide line was running there. Mitsubishi came into the plant through the joint venture Hoechst Diafoil, and in 1998 Mitsubishi Chemical took over the Hoechst shares (Mitsubishi Polyester Film, About us). Since then the manufacturer has been called Mitsubishi Polyester Film, while the brand has stayed.
In early 2026 a new line costing around EUR 120 million went into operation in the Kalle-Albert industrial park. It produces 27,000 tonnes of Hostaphan film a year and raises the previous volume of 50,000 tonnes by more than half (CHEManager, January 2026). For purchasing this means the film comes from a European plant with growing capacity, a point that counts in supply chain assessments.
Chemically, HOSTAPHAN is the same material class as Mylar, Melinex or Lumirror. What the generic material can do, where its temperature limit lies and how to select it is covered in the article on polyester film. This article covers what applies only to the brand: grades, data sheets, delivery programme.
The RN, RNK and WN grades carry electrical insulation
Mitsubishi offers HOSTAPHAN grades for printing, packaging and labels, matte and siliconised release films, lidding films and films with recycled content. Three of them are relevant for motors, transformers and coils. The letters identify the film, the number after them the thickness in micrometres: RN 50 is the transparent standard film in 50 µm.
| Grade | Structure and appearance | Thicknesses | Use in insulation |
|---|---|---|---|
| HOSTAPHAN RN | single layer, transparent, glossy | 50 to 500 µm | slot insulation, slot closures, phase insulation, layer insulation in transformers and chokes |
| HOSTAPHAN RNK | three-layer coextruded, high gloss, 90 % transparency | 12 to 100 µm | thin layer and turn insulation, insulating tapes, membrane switches |
| HOSTAPHAN WN | translucent white | 125 to 350 µm in the data sheet | end winding, single phase and slot insulation, chokes |
Sources: Mitsubishi, data sheets WN (02/24) and RNK (09/26), overview of universal films. Some descriptions call WN opaque. That is wrong, the film is translucent white. In the data sheet it is electrically on a par with RN, and a white ply in the slot is easier to spot than a transparent one.
Not every HOSTAPHAN is an insulating film. RNK 2600 is chemically pretreated for printing and metallising, WO is a white opaque print film for labels and cards, MT a matte film. These grades carry no thermal class in their data sheets. If a drawing only says “HOSTAPHAN” without a grade, we therefore ask before we slit.
HOSTAPHAN properties from the manufacturer's data sheet
The values below come from Mitsubishi's general data sheet and from the WN data sheet. They are typical values, not specification limits, as every Mitsubishi sheet states.
| Property | Value | Test standard, condition |
|---|---|---|
| Thermal class | B (130 °C) | VDE 0530, main list |
| Tensile strength | 200 N/mm² machine and transverse direction | ISO 527, 23 °C |
| Young's modulus | 4,500 N/mm² | ISO 527, 23 °C |
| Shrinkage | 1 to 3 % MD, 0 to 2 % TD; WN 1.0 and 0.8 % | DIN 40634, 150 °C, 15 min |
| Permittivity | 3.3 at 23 °C, 3.6 at 150 °C | DIN 40634, 50 Hz |
| Dissipation factor tan δ | 0.0020 at 23 °C, 0.0048 at 150 °C | DIN 40634, 50 Hz |
| Volume resistivity (WN 190 µm) | 1018 Ω·cm at 23 °C, 1012 Ω·cm at 150 °C | DIN 40634, DC |
| Glow discharge resistance | 900 min at 40 kV/mm | DIN 53485, on 36 µm |
| Glass transition, melting point | 70 °C, 260 °C | calorimetry |
| Thermal conductivity | 0.13 W/(m·K) | VDE 0304 |
| Density | 1.4 g/cm³ | ASTM D 1505 |
| Water absorption | 0.5 % after 4 days in water | ASTM D 570 |
Distributor sheets list two temperature figures side by side that do not mean the same thing. “Usable from -70 to 150 °C” describes the range in which the film does not fail in the short term. For design, the continuous rating of 130 °C per thermal class B applies. At the low end HOSTAPHAN is uncritical, Mitsubishi has tested it down to -196 °C. At the high end it stays dimensionally stable under pressure and tension up to 240 °C, and no flammable gases form up to 400 °C. These are reserves for fault conditions, not operating values.
One limit appears only in the small print: above about 100 °C, PET becomes brittle through hydrolysis in the presence of water vapour. For windings that run hot and humid, this rules HOSTAPHAN out even when the thermal class fits.
HOSTAPHAN breakdown voltage by thickness
Breakdown voltage rises with thickness, but more slowly than the thickness itself. Anyone who scales the kV/mm value of a thin film up to a thick one overestimates the insulation. The values for RNK, RN and WN at 23 °C and 50 Hz to DIN 40634:
| Grade and thickness | Breakdown voltage | converted |
|---|---|---|
| RNK 23 µm | 7.5 kV | around 326 kV/mm |
| RN 50 µm | 12 kV | 240 kV/mm |
| RN 75 µm | 16 kV | around 213 kV/mm |
| RN 100 µm | 19 kV | 190 kV/mm |
| RN 125 µm | 23 kV | 184 kV/mm |
| WN 125 µm | 22 kV | 176 kV/mm |
| WN 190 µm | 30 kV | around 158 kV/mm |
| WN 230 to 350 µm | above 30 kV | not quantified in the data sheet |
Sources: Mitsubishi, data sheets RNK and WN; RN according to manufacturer data in the SynFlex product data sheet (06/24). The WN data sheet also shows how strongly the conditions shift the value: the same 190 µm film withstands 30 kV at 50 Hz, 80 kV at DC and still 26 kV at 150 °C. Which test voltage the finished part has to hold in routine testing is a different question, answered in the article on voltage withstand. How the kV/mm value is measured is explained in the article on dielectric strength.
Where HOSTAPHAN sits in motors and transformers
Mitsubishi and the distributor data sheets name the same locations. They follow the thickness:
- In transformers, chokes and relays as core, layer and cover insulation, in thin grades from RNK 12 or RN 50. The ply between two winding layers is described in the article on layer insulation.
- In the stator of motors and generators as slot insulation, as slot closure and as phase insulation in the end winding, depending on machine size as RN or WN up to 350 µm.
- As the PET core in laminates such as DMD and NMN, which take the same film into higher thermal classes.
- In flexible printed circuits, flat cables and membrane switches as the carrier film, there mostly in thin RNK grades.
HOSTAPHAN is compatible with the impregnating resins used in electrical machine building: polyester and epoxy resins, polyurethane varnishes and isocyanates do not attack it. Resins containing amines or phenol, on the other hand, have to be tested first, because free phenol damages the film under heat (Mitsubishi, WN data sheet and General Technical Data). This question belongs in every approval of a new winding.
Converting HOSTAPHAN: slitting, stamping, forming
Mitsubishi delivers mother rolls on cores with an inner diameter of 152.4 mm. What gets installed is a strip in slot width or a stamped part with a folded edge. In between lies the converting, and the WN data sheet gives three clear pointers for it: stamping is done in a shear cut, the film can be formed cold and warm, and with punch and die it can be deep drawn to about 15 mm given sufficient dwell time.
In contract slitting we slit HOSTAPHAN into rolls from 5 to 1,600 mm wide with a width tolerance of ±0.1 mm, wound on cores of 25, 55, 76 or 152 mm. Mother rolls up to 1,000 kg run at up to 400 m per minute, depending on the material. In stamping and forming we process film from 0.023 to 3.0 mm thick into parts up to 1,000 x 2,000 mm, with steel rule dies for samples and small batches and solid steel tools for series with tight tolerances. We form the folded edges of slot insulation under heat so that they hold and do not spring back.
Mitsubishi sets clear storage rules, and we follow them: dry and dust-free below 30 °C, in the original packaging, at least 24 hours in the climate of the production hall before processing, and processed within a year of delivery. A mother roll is carried on a steel bar through the core so that the outer layers are not dented.
HOSTAPHAN at GOBA: the brand on the drawing is the brand in the part
We are the largest European converter of Mitsubishi Hostaphan in thick films and work with all well-known European film manufacturers at the same time. That is why we supply the other brands such as Mylar just as readily. You can get HOSTAPHAN from us as a roll, sheet, cut piece, stamped part or formed part, from a single piece, and within two weeks at most when the material is in stock.
One objection comes up regularly from purchasing: if Mylar and HOSTAPHAN are the same material class, why not take whichever film is cheaper at the moment? For many parts that works, and we tell you so openly. But if the drawing says “HOSTAPHAN RN”, there is often a UL listing behind it (for HOSTAPHAN under file no. E53895) or a customer approval of the insulation system. Then we supply exactly that brand, with no silent substitution. To get the enquiry right the first time, we need:
- Grade and thickness, for example RN 125 or WN 190, and whether the brand is mandatory.
- Delivery form: slit roll with width and core, cut piece or stamped part to drawing.
- Tolerances on width and contour, for formed parts the position of the folded edges.
- Quantity per call-off and annual demand, so that we choose roll or tool correctly.
An overview of the other materials we carry alongside polyester film is on the page about our insulation materials.
