KOCETAL K300 vs Formosa FM090 vs DURACON M90: Picking the Right Medium-Viscosity POM

A gear shop in India once ordered a container of acetal copolymer based on a 5% price discount, without checking whether the grade matched the melt flow of the material in its molds. The parts filled fine but the cycle time stretched by 8%, and the dimensional yield dropped until the shop re-tuned every process parameter. The resin was not bad; it was simply the wrong viscosity for that tool.

KOCETAL POM K300, Formosa POM FM090, and DURACON M90 are three of the most widely specified medium-viscosity acetal copolymers in the world. They compete in the same application space, and buyers often treat them as identical. They are close cousins, but each has characteristics worth weighing before you standardize on one.

This guide compares the three grades on melt flow, mechanical properties, processing behavior, supply, and price, so you can pick the one that fits your production reality rather than your habit.

1. Why Medium-Viscosity POM Is the Workhorse

Medium-viscosity acetal copolymer, with a melt flow rate of roughly 8 to 10 g/10 min, sits in the sweet spot of the POM range. It flows well enough for complex molds yet retains enough molecular weight for good mechanical properties.

This viscosity class covers the majority of injection-molded POM parts: gears, bearings, pulleys, housings, fasteners, and automotive components. Lower-viscosity grades fill thin walls faster but give up toughness; higher-viscosity grades are tougher but harder to fill. The medium class avoids both extremes, which is why it appears on more drawings and BOMs than any other POM viscosity.

Because the medium range is so popular, every major POM producer offers a flagship grade in it. K300, FM090, and M90 are those flagships, which is why they appear side by side in sourcing conversations. For a molder, the practical question is not which one is chemically better, but which one is available, consistent, and validated in your process, because the property differences are small enough that supply and process fit decide the outcome.

2. The Three Contenders: K300, FM090, and M90

KOCETAL POM K300 is produced by Korea Engineering Plastics, or KEP, a joint venture that licenses technology from a major Japanese producer. It is positioned as a general-purpose injection molding grade for precision mechanical parts.

Formosa POM FM090 comes from Formosa Plastics Corporation in Taiwan, China, and is a medium-viscosity copolymer aimed at the same broad application range. It has built a strong following among molders who value stable supply and consistent lot quality.

DURACON M90 is the long-standing flagship of Polyplastics, a global joint venture that helped establish acetal copolymer technology. M90 has decades of field history and is the reference grade many engineers compare everything else against.

All three are acetal copolymers, so their chemistry family is the same. The differences lie in the exact formulation, stabilizer package, and the lot-to-lot discipline of each producer. For a buyer, those differences translate into how consistently the resin processes and how much paperwork and testing you need to manage the supply. In practice, the stabilizer package also influences color stability and long-term aging, which matters for parts that must keep their appearance.

3. What Melt Flow Rate Tells You

The melt flow rate, or MFR, is the first number to compare. All three grades sit in the 8 to 10 g/10 min window, which is why they are considered interchangeable in many tools.

Within that window, small differences matter for high-cavity molds and thin-wall parts. A grade at 9.5 g/10 min fills slightly faster than one at 8.5 g/10 min, which can shorten cycle time on a 64-cavity gear mold.

The practical approach is to check the actual MFR value on the certificate for each lot you receive, because producers hold a tolerance band rather than a single number. Consistent MFR from lot to lot is often more valuable than the nominal value itself.

MFR is measured under standardized conditions, typically at 190°C with a 2.16 kg load, and it is the quickest single check that a lot matches your specification. A certificate that lists the MFR and the test standard lets you compare lots across producers fairly, which is exactly what you want when qualifying a second source.

4. Mechanical Properties Side by Side

The mechanical properties of the three grades are close because they share the same viscosity class and polymer family. Tensile strength, modulus, and impact values cluster within a few percent of each other.

The table below shows typical values to give you a working comparison. Always verify against the current datasheet from the producer before finalizing a design.

The small differences in elongation reflect formulation choices rather than quality. A part that sees repeated flexing may favor the grade with higher elongation, while a part that must resist creep favors higher modulus. In practice, these differences rarely change a design decision; they matter most when a part is running at the edge of the material's capability.

5. Thermal and Dimensional Behavior

All three grades are acetal copolymers with melting points near 165°C and similar heat deflection temperatures around 100 to 110°C at low load. Their thermal behavior is close enough that a mold tuned for one runs the others without redesign.

Shrinkage is the number to watch for dimensional parts. The three grades list mold shrinkage around 1.8 to 2.0%, with small grade-to-grade variations. If you are swapping grades on an existing tool, verify the shrinkage value on the datasheet before cutting steel.

Moisture absorption is low and similar across the three, around 0.2% at saturation, so dimensional stability in humid environments is comparable. This is one of the reasons all three perform well in gears and precision mechanisms.

Crystallization behavior is worth a mention because it affects cycle time. Acetal copolymers crystallize quickly compared with many engineering plastics, which is why POM parts eject fast, and the three grades behave similarly in this regard. Mold temperature control remains the main lever for managing crystallinity and the resulting dimensions.

6. Processing Characteristics

Recommended melt temperatures are similar, roughly 190 to 220°C for all three, and mold temperatures around 60 to 100°C are typical. Processors switching among them usually need only minor tweaks. A useful habit is to record the exact settings during the first trial with a new grade, because the optimal window for one lot can guide the setup for the next source.

Where they can differ is in flow behavior and crystallization rate, which show up as cycle time and surface quality. Some molders report subtle differences in fill pressure and flash tendency between the three, which is why a mold trial with the actual grade is the reliable way to confirm.

All three require the same discipline that all POM demands: avoid overheating, control residence time to limit formaldehyde release, and keep the melt temperature stable across the barrel. None of the three needs intensive pre-drying for most applications, though keeping the bags sealed until use is still good practice.

7. Availability and Supply Chain Considerations

Supply reliability is often the deciding factor in practice. DURACON M90 has the longest market history and the widest global distribution network, which makes it easy to source in most regions but also means it is widely used and periodically tight in supply.

KOCETAL K300 benefits from Korean production capacity and strong regional distribution in Asia, with good availability in nearby export markets. Formosa FM090 benefits from Taiwanese production and competitive pricing, and it has gained share among buyers looking for a stable secondary source.

At Ailide Polymer (Jiangsu) Co Ltd, we carry KOCETAL POM K300 and Formosa POM FM090 as core stock grades, which gives buyers a practical choice between two proven medium-viscosity copolymers with different supply chains. A secondary source is valuable insurance in a market where resin availability fluctuates. Our material specialists at Ailide can also compare the lot certificates side by side when you qualify a new source.

8. Price Comparison and Total Cost

Prices for the three grades track each other closely, with differences of a few percent driven by brand, region, and purchase volume. Premiums for the most established brand are not automatic; regional supply and freight often matter more than the brand itself.

Total cost includes more than the per-kg price. Consistent MFR reduces scrap and rework, stable supply reduces emergency air-freight costs, and a grade that runs at the same cycle time as your current material saves nothing extra but avoids disruption. Buyers who have been burned by a cheap lot that shifted their process know how quickly apparent savings evaporate.

The practical buying advice is to compare landed cost for your region and your volume, and to weigh supply security as heavily as the price per kilogram. A few cents per kg saved on a material that delays your line is a poor trade. At Ailide Polymer, we publish landed-cost estimates for both grades so buyers can see the full picture before choosing.

9. How to Choose: Application-Driven Selection

The honest answer is that for most medium-viscosity applications, any of the three grades will perform well. The selection is driven by supply, price, and your existing process validation rather than by dramatic property differences.

If your customer or OEM has approved a specific brand, stay with it to avoid re-qualification. If you have design freedom, choose based on availability in your region and run a mold trial to confirm cycle time and dimensional yield.

Many buyers standardize on one primary grade and qualify a second as backup. That is a sound strategy, and carrying K300 and FM090 together is exactly the kind of dual-source arrangement that protects production schedules. Ailide Polymer (Jiangsu) can quote both grades for the same part, so the backup decision is made with real numbers rather than speculation.

10. FAQ About K300, FM090, and M90

10.1 Are KOCETAL K300 and DURACON M90 interchangeable?

For most applications, yes. Both are medium-viscosity acetal copolymers with similar melt flow, mechanical properties, and shrinkage, so an existing M90 mold generally runs K300 with minor adjustments. Before swapping, verify the datasheet values and run a short mold trial, because fill behavior and cycle time can differ subtly. If a customer specification names a specific brand, obtain approval before substituting, and keep the qualification records for the audit trail.

10.2 Which grade is cheaper: FM090 or K300?

Prices vary by region, volume, and market conditions, and the gap between FM090 and K300 is usually only a few percent. FM090 has historically been competitive in Asian markets, while K300's price depends on Korean production economics and freight. The right way to compare is a landed-cost quotation for your destination, not a per-kg list price, because logistics can erase a small price advantage.

10.3 Can I use these grades for gears and bearings?

Yes, medium-viscosity acetal copolymers are the standard choice for injection-molded gears, bearings, and sliding parts. Their combination of stiffness, low friction, dimensional stability, and fatigue resistance suits precision mechanisms. Choose the grade based on supply and your validated process, and design the gear with proper root radius and gating to avoid stress concentrations. For high-speed or high-load gear trains, confirm the wear and fatigue data on the datasheet before finalizing the material.

10.4 How do I verify the quality of a POM shipment?

Start with the certificate of analysis, which should show the melt flow rate, density, and tensile values for the specific batch. Check that the batch number on the certificate matches the labels on the bags, and confirm the moisture content is within spec. For critical applications, run a small molding trial on arrival and compare cycle time and dimensions with your reference material.