Search “PMMA melting point” and you will find five different answers that cannot all be correct. Wikipedia says 130 to 140 °C. Chinese molding pages say the melting temperature is greater than 160 °C.
Princeton’s glossary says about 200 °C. AZoM lists a 220 to 240 °C melt range. And a handful of technical sources say acrylic has no melting point at all.
One of those numbers is a softening range. One is a flow onset. One is a processing setpoint. One belongs to a crystalline form you will never buy. And one is essentially the truth.
The problem is that no single page tells you which is which, so engineers pick the number that looks most like a “melting point” and design against it.
Here is the straight answer. PMMA, better known as acrylic, is an amorphous thermoplastic. It has no true melting point.
It softens above its glass transition temperature of about 105 °C (221 °F), begins to flow at roughly 160 °C, is molded at 210 to 270 °C, and starts to depolymerize above about 270 °C. The number you should actually design against is not a melting point at all.
This guide resolves the contradiction, gives you the real acrylic melting point values in °C and °F, explains where each quoted figure comes from, breaks PMMA down by grade, and shows what to verify before you buy. We supply branded prime acrylic from Suzhou with a Certificate of Analysis on every batch. If you already know your grade, request a PMMA resin quote and our team responds within 24 hours.
Does PMMA Have a Melting Point?
No. PMMA (acrylic) has no true melting point. It is an amorphous thermoplastic with no crystalline regions to melt, so it softens gradually above its glass transition temperature of about 105 °C (221 °F), begins to flow at roughly 160 °C (320 °F), and is processed at 210 to 270 °C (410 to 518 °F). Reported “melting points” of 130 to 140 °C are softening ranges, not a thermodynamic Tm.
That is the direct answer behind searches for “does PMMA have a melting point,” “does acrylic melt,” and “what temperature does acrylic melt.” It is a real materials distinction, not a technicality.
A semi-crystalline plastic such as POM or nylon packs its chains into ordered crystals that break down at one sharp temperature. Melt the crystals and the material turns to liquid.
PMMA’s chains are bulky and irregular, so they never organize into crystals in the first place. There is nothing to break down all at once. What you get instead is a gradual loss of stiffness as the material heats.
Why PMMA Has No Melting Point
PMMA is built from methyl methacrylate units with a methyl group and a bulky ester side group hanging off every repeat unit. Those side groups jam the chain and prevent any regular packing. The chains freeze in random, tangled positions as the part cools, because cooling is far too fast for them to order themselves.
That disordered structure is exactly why acrylic is transparent. Crystalline regions scatter light, and amorphous ones do not. The same physics that makes PMMA clear, with light transmission around 92%, is the physics that leaves it without a melting point. Wikipedia’s entry on poly(methyl methacrylate) confirms the amorphous structure and the ~105 °C Tg, though its infobox still lists a 130 to 140 °C “melting point” that the body text does not defend.
Thermal analysis proves the point. A semi-crystalline polymer shows a sharp melting endotherm on a DSC curve. Measured that way, a PMMA melting temperature simply does not appear. NETZSCH’s PMMA thermal analysis lists a melting temperature of “dash,” meaning none, and shows a curve typical of amorphous materials with a Tg step and no melt peak.
One honest footnote. A stereoregular, isotactic form of PMMA can be crystallized in a laboratory from solution, and its extrapolated equilibrium melting temperature is about 171 °C. That is academic chemistry. No commercial acrylic pellet behaves this way, and it should not enter your design calculations. Our plastic melting point chart puts PMMA alongside every other material in the cluster if you want the master reference.
Where the Five Quoted “Melting Points” Come From
This is the part no other page explains, and it is the whole reason the search results contradict each other.
- 130 to 140 °C (265 to 285 °F). The softening range quoted by Wikipedia and the INRS plastics database. This is the number most searchers see first. It is not a melting point, it is the region where the material stops behaving like a rigid solid.
- About 160 °C (320 °F). The flow onset, usually written on datasheets as “melting temperature greater than 160 °C.” This is where PMMA begins to flow under load. It is a processing landmark, not a phase change.
- About 171 °C (340 °F). The crystalline melting temperature of isotactic PMMA, a lab-only value discussed above.
- 200 to 240 °C (392 to 464 °F). The processing and melt range reported by AZoM and several reference databases. This is a machine setpoint, not a material transition.
- Above 270 °C (518 °F). The depolymerization and degradation onset, where PMMA starts breaking back down toward methyl methacrylate monomer.
Treat 130 to 140 °C as a softening landmark, 160 °C as the flow onset, and 210 to 270 °C as the processing window. Never treat any of them as a service limit.
The PMMA Melting Point Numbers That Actually Matter
Five temperatures define how acrylic behaves in a mold and in service. Each answers a different question, and confusing them is the source of nearly every acrylic thermal mistake we see.
- Glass transition (Tg): about 105 °C (221 °F), the real design ceiling.
- Softening and Vicat range: about 96 to 108 °C, when the part starts to give under load.
- Datasheet “melting point”: 130 to 140 °C, the mislabeled softening range.
- Processing melt temperature: 210 to 270 °C, what the machine is actually set to.
- Decomposition onset: above 270 °C, where the polymer depolymerizes.
Glass Transition Temperature (Tg): About 105 °C
Standard atactic PMMA has a glass transition temperature near 105 °C, which is 221 °F. Reported values run from about 90 to 110 °C depending on grade, molecular weight, moisture, and test method, and heat-resistant grades push toward 120 °C. Tests follow ASTM D3418 or ISO 11357.
Tg is the temperature at which the amorphous polymer shifts from a rigid glass to a soft, rubbery state. Above it, the modulus drops sharply, creep accelerates, and optical distortion sets in. This is the number that actually limits a PMMA part in hot service, which is why engineers should be searching for acrylic’s glass transition temperature rather than its melting point. We cover the full Tg picture, including tacticity and the grade ladder, in our dedicated guide to PMMA glass transition temperature.
PMMA Softening Temperature and Vicat Softening Point
The PMMA softening temperature sits around 96 to 108 °C (205 to 226 °F) for standard optical grades, measured as the Vicat softening temperature to ISO 306 or ASTM D1525. That test tracks how deep a loaded needle sinks into the surface as the material heats. It is a practical proxy for “when does this part start to give,” not a melting temperature and not a design limit. If you need the difference between softening, melting, and deflection spelled out, our heat deflection temperature versus melting point hub walks through which number to specify for which load case.
Heat Deflection Temperature (HDT)
HDT is the temperature at which a loaded test bar deflects by a set amount, measured per ISO 75 or ASTM D648. Unfilled PMMA reaches about 95 to 103 °C, higher at 0.45 MPa than at 1.8 MPa, and some references cite roughly 96 °C at 1.82 MPa. HDT is the number to put in a specification whenever a part carries a load at temperature. Melting point tells you nothing about that.
Continuous Service Temperature: About 65 to 80 °C
This is the trap. Acrylic’s quoted “melting point” is not a service limit, and neither is its Tg. The usable continuous ceiling for standard PMMA is about 65 to 80 °C depending on load and grade, with some sources rating maximum operating temperature as low as 50 °C.
Keep continuous service well below Tg. Optical and aesthetic parts derate further than structural ones, because a part that looks slightly hazy or warped fails even if it has not structurally failed.
Thermal Decomposition: Above About 270 °C
Above roughly 270 °C, PMMA depolymerizes back toward MMA monomer. It releases vapor, causes bubbles and silver streaks, and hazes the melt. Visible degradation begins before bulk decomposition, which is why the practical processing ceiling is set well below the TGA onset. NETZSCH reports TGA decomposition in the 360 to 390 °C region, but no molder runs acrylic anywhere near that.
PMMA Thermal Properties at a Glance
| Property | Value | What it actually means |
|---|---|---|
| True melting point (Tm) | None (amorphous) | No crystalline phase to melt |
| Glass transition (Tg) | ~105 °C (221 °F) | The real design ceiling |
| Softening / Vicat (VST) | ~96 to 108 °C | Starts to give under load |
| Datasheet “melting point” | 130 to 140 °C (265 to 285 °F) | Softening range, not a Tm |
| Flow onset | ~160 °C (320 °F) | Begins to flow |
| HDT at 1.8 MPa | ~95 to 103 °C | Load-bearing thermal limit |
| Continuous service | ~65 to 80 °C | Hold well below Tg |
| Processing melt temp | 210 to 270 °C | What the machine is set to |
| Mold temperature | 60 to 90 °C | Controls stress and optical quality |
| Drying | 80 to 90 °C for 2 to 4 h to under 0.04% | Mandatory, splay and haze risk |
| Decomposition onset | Above ~270 °C (TGA 360 to 390 °C) | Depolymerization to MMA |
Why the PMMA Processing Temperature Runs 210 to 270 °C
If PMMA starts flowing at 160 °C, the obvious question is why anyone runs a barrel at 240 °C. The answer is melt viscosity, and it is the same reason PC runs at 300 °C.
PMMA’s rigid, bulky side groups make its melt thick. Heat is what thins it. Raising the melt temperature drops the viscosity enough for the polymer to fill a cavity under realistic injection pressures, and PMMA is strongly shear-thinning, so injection speed matters as much as temperature.
The 210 to 270 °C window, typically 210 to 250 °C with optical grades at the upper end, is the compromise where acrylic flows well without degrading. Mold temperature is the other half: 60 to 90 °C controls molded-in stress and protects optical quality.
Residence time matters as much as temperature. Hold PMMA no longer than 10 minutes at 260 °C, or 8 minutes at 270 °C, because depolymerization begins once the melt sits too long at the top of the window. A hot barrel with a stalled cycle is how a clear part becomes scrap.
Extrusion runs cooler, about 160 to 220 °C, and thermoforming sits around 130 to 160 °C. Those windows are not transferable, and each one is a melt or forming setpoint, never a “melting point.”
Drying Is Mandatory, Not Optional
PMMA is hygroscopic. It absorbs moisture from the air, and that water does two damaging things during molding. It flashes to steam at the gate, causing splay marks and bubbles, and it plasticizes the melt, so the part comes out hazy.
Dry acrylic at 80 to 90 °C for 2 to 4 hours in a dehumidifying or desiccant dryer, targeting under 0.04% moisture. A hot-air dryer is not enough. This is also why the melting point number alone can never tell you how to run a process. A part molded from wet resin can satisfy every temperature on the datasheet and still fail optical inspection.
Priya, a process engineer at a lighting-components molder in Penang, learned this on a light-guide run. Her first production batch came out with faint silver streaks and a measurable haze that failed the customer’s optical spec. The barrel temperatures were perfect.
The dryer had been set to a 60 °C hot-air cycle overnight, and the resin had never gotten dry enough. Switching to a desiccant dryer at 85 °C for three hours cleared the streaks on the next shift.
Annealing and Stress Relief
Annealing below Tg, typically around 80 to 95 °C, relieves molded-in stress and improves dimensional and optical stability without softening the part into the rubbery state. It is a common step for parts that will see solvents, load, or tight tolerances, and it is another reminder that PMMA is managed through its Tg and processing window, not through any melting temperature.
PMMA Melting Point and Thermal Limits by Grade
Not every acrylic grade shares the same thermal profile. None of them gains a melting point. What changes is the glass transition temperature, the HDT, and the processing window.
| Grade family | Tg (°C) | HDT at 1.8 MPa (°C) | Process melt (°C) | Typical applications |
|---|---|---|---|---|
| Standard optical (PLEXIGLAS® 7N/8N, Acrypet® MD) | ~104 to 112 | ~95 to 103 | 210 to 260 | Light guides, lenses, display covers, signage, glazing |
| Impact-modified | ~95 to 105 | ~85 to 95 | 210 to 250 | Automotive interior trim, safety covers, housings |
| Heat-resistant (PLEXIGLAS® Heatresist FT15) | ~121 | ~105 to 115 | 230 to 270 | LED and automotive lighting, near-heat optical parts |
| Cast and extruded sheet | Varies by thickness | Varies | Thermoformed 130 to 160 | Signage, glazing, fabrication, displays |
Confirm these values against the manufacturer datasheet for the exact grade before you commit to a design. Grade families vary within themselves, and a suffix can change the thermal profile. One honest caveat on the heat-resistant line: a higher-Tg acrylic still has no melting point. The upgrade raises Tg and HDT, and it does not create a Tm.
PMMA Melting Point vs. Other Plastics
The fastest way to see why acrylic’s melting point question is the wrong question is to compare it against materials that actually have one.
| Material | Structure | Tm (°C) | Tg (°C) | HDT at 1.8 MPa (°C) | Process melt (°C) | Service (°C) |
|---|---|---|---|---|---|---|
| PMMA | Amorphous | None (softens ~160) | ~105 | ~95 to 103 | 210 to 270 | 65 to 80 |
| PC | Amorphous | None (softens ~215 to 230) | ~147 | ~125 to 135 | 280 to 320 | 115 to 125 |
| ABS | Amorphous | None | ~105 | ~85 to 100 | 200 to 250 | 60 to 80 |
| POM | Semi-crystalline | ~165 to 175 | ~-60 | ~100 to 110 | 185 to 210 | 80 to 120 |
| PA66 | Semi-crystalline | ~255 to 265 | ~50 to 65 (dry) | ~70 to 100 | 270 to 300 | 80 to 120 |
| HDPE | Semi-crystalline | ~130 to 137 | ~-120 | ~45 to 70 | 180 to 260 | 60 to 80 |
The pattern is clear. The melting point column is empty for PMMA, PC, and ABS, because all three are amorphous. They are compared on Tg and HDT instead. Meanwhile POM, PA66, and HDPE have real melting points.
That is the single most useful frame for anyone confused by an acrylic melting point search result.
PMMA vs. PC for Transparent Parts Near Heat
Acrylic and polycarbonate compete for the same optical applications, and the decision usually comes down to heat. PC wins on temperature, with a Tg of about 147 °C against PMMA’s roughly 105 °C, and it wins on impact strength. PMMA wins on scratch resistance, UV stability, optical clarity, and cost.
The honest guidance is direct. For a transparent part that must hold up above about 80 °C in continuous service, specify PC or a heat-resistant PMMA grade, not standard acrylic. Our polycarbonate melting point article covers the other side of that comparison, and our PC resin page lists the grades we supply when acrylic is the wrong answer.
PMMA vs. ABS at Elevated Temperature
Neither material has a melting point, and both sit near a 105 °C Tg, so the thermal chart barely separates them. The real decision is clarity and UV stability on the PMMA side against toughness and cost on the ABS side. If a warm part needs to stay transparent and weather outdoors without yellowing, acrylic is the usual choice.
Why PMMA Thermal Consistency Matters for Buyers
Thermal data only helps if it describes the batch you actually mold. This is where the difference between branded prime resin and unknown compound shows up on the shop floor.
Batch-to-Batch Variation Is a Red Flag
Branded manufacturers publish consistent Tg, HDT, Vicat, and melt flow baselines for each grade. When a supplier’s numbers drift between shipments, it usually signals off-spec compounding, regrind contamination, or material that is not the branded grade it claims to be.
Because PMMA has no melting point, you cannot validate it by testing a melting temperature. Validate Tg, HDT, Vicat, and MFR against the published baseline instead. For an optical polymer, run the optical checks too, because a regrind-contaminated or blended lot often shows up as reduced light transmission or a raised yellowness index before it shows up in the mechanicals.
What to Check on the Certificate of Analysis
The COA is your verification tool. Confirm the grade designation and manufacturer, so you know exactly which branded acrylic you are buying. Check the thermal baseline of Tg, HDT, Vicat, and melt flow rate, plus density as a secondary identity check.
For optical grades, confirm light transmission above 92% and haze under 1% on premium material, along with the yellowness index. Finally, check the lot and batch number, plus RoHS and REACH statements where your market requires them.
A COA is only as valuable as the brand behind it. We supply branded prime acrylic rather than commodity compound, and every batch from our Suzhou warehouse ships with a manufacturer-issued Certificate of Analysis, the MSDS, the commercial invoice, and the packing list.
Sourcing PMMA from China
If you source acrylic from China, buy branded prime resin from a supplier who can prove it. Our location in Suzhou, minutes from the Port of Shanghai, keeps export lead times at 7 to 14 days depending on destination, with FOB Shanghai as the standard term and a 25 kg minimum order.
That small minimum makes qualification practical. Order 25 kg from the same lot your production material will come from, run your own thermal and optical checks against the COA, and confirm the grade before committing to volume. Our PMMA material properties guide lists the branded grades and documentation we provide for optical, signage, automotive, and consumer applications.
Frequently Asked Questions
Does PMMA have a melting point?
No. PMMA, or acrylic, is amorphous and has no true melting point. It softens above its glass transition temperature of about 105 °C and begins to flow at roughly 160 °C.
What is the melting point of acrylic in Celsius?
There is no true melting point. The figure most often quoted, 130 to 140 °C, is a softening range, not a thermodynamic melting transition.
What is the melting point of acrylic in Fahrenheit?
About 265 to 285 °F, which is the same 130 to 140 °C softening range. Commercial acrylic has no true Tm in either scale.
Why is PMMA’s melting point listed as 130 to 140 °C if it has no melting point?
That number marks where acrylic stops behaving like a rigid solid. It is a softening landmark, not a melting point, and it sits well below the 210 to 270 °C a molder actually runs.
Why do some sources say acrylic melts at 160 °C?
That is the flow onset, the temperature at which PMMA begins to flow under load. Datasheets phrase it as “melting temperature greater than 160 °C,” which is a processing landmark, not a phase change.
At what temperature does PMMA soften?
Softening begins around 96 to 108 °C for standard optical grades. The formal Vicat softening temperature is tested to ISO 306 or ASTM D1525.
Is acrylic safe at 80 °C or 100 °C?
At 80 °C, standard acrylic is usually fine for light-load, non-optical-critical parts. At 100 °C you are close to the HDT and above the practical service ceiling, so expect creep and distortion. For sustained service above about 80 °C, specify a heat-resistant grade or move to PC.
What temperature should PMMA be processed at?
Injection molding melt temperature is 210 to 270 °C, typically 210 to 250 °C, with mold temperature at 60 to 90 °C. Extrusion runs 160 to 220 °C, and thermoforming runs 130 to 160 °C.
Does PMMA need to be dried before molding?
Yes, always. PMMA is hygroscopic. Dry at 80 to 90 °C for 2 to 4 hours to below 0.04% moisture in a desiccant dryer. Molding wet acrylic causes splay, bubbles, and haze.
Is PMMA better than polycarbonate for high-temperature applications?
No. PC’s Tg of about 147 °C beats acrylic’s roughly 105 °C, and its service ceiling of 115 to 125 °C beats PMMA’s 65 to 80 °C. Acrylic wins on scratch resistance, UV stability, clarity, and cost, not on heat.
Is PMMA amorphous or crystalline?
PMMA is amorphous. That is why it is transparent and why it has no melting point. Only a lab-made isotactic form crystallizes, and it is not commercially available.
Conclusion
The PMMA melting point is one of the most misunderstood numbers in engineering plastics, and the truth is simpler than the search results suggest. Acrylic is amorphous, so it has no true melting point.
It softens above a glass transition temperature of about 105 °C (221 °F), flows from roughly 160 °C, is molded at 210 to 270 °C, and depolymerizes above about 270 °C. The numbers that actually govern a design are Tg, HDT of about 95 to 103 °C at 1.8 MPa, and continuous service near 65 to 80 °C. Heat-resistant grades raise Tg and HDT, never Tm.
Treat the datasheet’s 130 to 140 °C as a softening range, not a service limit, and never as a setpoint. Validate your incoming resin on Tg, HDT, Vicat, and melt flow rather than a melting temperature that does not exist, and buy branded prime acrylic with a traceable Certificate of Analysis so the batch behaves like the datasheet.
We supply branded prime PMMA, including standard optical, impact-modified, and heat-resistant grades, from leading manufacturers with full COA documentation, a 25 kg minimum order, and FOB Shanghai pricing. Tell us your application, your service temperature, and your optical requirements, and we will recommend the right branded grade, including an honest redirect to PC or a heat-resistant acrylic if your part runs hotter than standard PMMA should. To learn more about ABS Melting Point in Fahrenheit and POM Melting Point, please refer to our accompanying guide.
Request a PMMA resin quote and get a recommendation backed by real datasheets, not a number that was never a melting point.
