What Are the Real-World Technical Specs of Acrylic That Every Engineer Should Know?

Picking the right plastic is a minefield. Acrylic shines, but is it right for your part? Understanding its core mechanical, thermal, and optical traits is absolutely vital before you sign off on that design.

Acrylic (PMMA)¹ boasts superior optical clarity², good mechanical strength³ with excellent surface hardness, decent thermal stability for many applications, and reliable electrical insulation, making it a versatile engineering thermoplastic.

I’ve been working with acrylic for years here at CKMOLD, and I’ve seen it used in countless applications, from simple display windows to complex optical lenses for your industry, Michael. Its balance of properties is often what makes it a winner, but knowing the specific values and how they translate to performance is key. It’s not just "clear plastic"; it’s a material with a distinct personality. Let’s unpack its full technical datasheet so you can make informed decisions.

Alright, so you’re considering acrylic for your next project. You’ve heard it’s clear, maybe a bit brittle, but what does that really mean when it comes down to numbers and real-world performance? I’m going to break down the key mechanical, optical, and thermal properties in a way that hopefully makes sense for your design challenges. We’ll look at the data, sure, but more importantly, what that data means for your components. Stick with me, and you’ll get a much clearer picture (pun intended!) of what acrylic can truly offer.

How Strong is Acrylic, Really, When We Talk Mechanical Specs?

You need parts that won’t snap, bend too easily, or scratch up on day one. So, when we say acrylic is "strong," what are the actual engineering metrics behind that statement, and where are its limits?
Acrylic offers good tensile and flexural strength, outstanding surface hardness (scratch resistance), but exhibits lower impact strength compared to tougher plastics like polycarbonate, making it somewhat brittle and notch-sensitive.
I remember a client, much like yourself, Michael, who was designing a protective cover. They loved acrylic’s clarity and hardness, but the initial design had some sharp internal corners. During prototype testing, we saw tiny cracks forming right at those stress points under minor impacts. A quick redesign with smoother radii, based on understanding its notch sensitivity, solved the problem entirely. It’s about knowing how to design for the material.
Let’s dig into the key mechanical figures:

Key Mechanical Values and Their Significance

• Tensile Strength: This tells you how much pulling force acrylic can withstand before it starts to deform permanently or break. Typically, PMMA sits in the 60-80 MPa (8,700-11,600 psi) range. This is quite respectable for a thermoplastic and means it can handle decent static loads. For perspective, general-purpose ABS might be around 40-50 MPa.
• Flexural Strength: This measures its resistance to bending. Acrylic usually shows flexural strength between 90-120 MPa (13,000-17,400 psi). Again, pretty good, meaning it can resist breaking when bent, up to a point.
• Impact Strength (Notched Izod): This is where acrylic shows its more "delicate" side. Standard acrylic has a notched Izod impact strength of around 15-30 J/m (0.3-0.6 ft-lb/in). This is significantly lower than, say, polycarbonate (which can be 600-800 J/m). This means if there’s a sharp notch or a sudden, hard impact, acrylic is more prone to fracture. We always tell clients: avoid sharp corners if impact is a concern!
• Surface Hardness: Acrylic shines here! With a Rockwell Hardness typically in the M80-M100 range, it’s one of the hardest thermoplastics. This translates to excellent scratch resistance compared to many other clear plastics. That’s why it’s great for displays and cosmetic parts.

• Modulus of Elasticity (Tensile Modulus): This indicates stiffness. For acrylic, it’s around 2.4-3.3 GPa (350,000-480,000 psi). It’s fairly rigid, which is good for maintaining shape but also contributes to its brittleness – less "give" before it breaks.	Mechanical Property	Typical PMMA Value Range	Implication for Your Designs, Michael
  Tensile Strength	60-80 MPa (8,700-11,600 psi)	Good for static loads, less so for high tensile stress apps.
  Flexural Strength	90-120 MPa (13,000-17,400 psi)	Resists bending well under moderate loads.
  Notched Izod Impact	15-30 J/m (0.3-0.6 ft-lb/in)	Key weakness! Design to avoid impacts, add radii, or consider impact-modified grades.
  Surface Hardness (Rockwell)	M80-M100	Excellent scratch resistance, great for aesthetic surfaces.
  Tensile Modulus	2.4-3.3 GPa (350-480 ksi)	Quite rigid, maintains shape but can be brittle.

  So, the takeaway for you, Michael, is that acrylic is strong in terms of resisting pulling, bending, and especially scratching. But you have to be mindful of its lower impact strength and notch sensitivity. Smart design – like generous fillets and avoiding stress concentrators – is your best friend when working with acrylic. For really tough applications, we might look at impact-modified grades or even other materials, but for many consumer electronics components where clarity and scratch resistance are paramount, standard acrylic, designed correctly, is fantastic.

  What Makes Acrylic So Exceptionally Clear From an Optical Standpoint?

  You need your components to be crystal clear, perhaps for a display, a lens, or a light pipe. Acrylic is famous for its optical properties, but what are the specific characteristics that make it so good?
  Acrylic (PMMA) achieves its outstanding optical performance through a high light transmittance of up to 92%, a refractive index close to glass (around 1.49), very low haze, and excellent UV stability, preventing yellowing over time.

I’ve lost count of the number of times clients have been amazed by the clarity of a well-molded acrylic part from CKMOLD. For one project involving intricate light guides for an automotive display, the client was initially skeptical about using plastic. When they saw the light transmission and uniformity we achieved with acrylic, they were sold. It’s not just "see-through"; it’s about how efficiently and faithfully it handles light.
Let’s break down these optical superpowers:

Deep Dive into Optical Performance

• Light Transmittance: This is a big one. Standard clear acrylic can transmit up to 92% of visible light. This is often better than standard glass and most other transparent plastics! For your applications, Michael, this means brighter displays, more efficient light piping, and clearer views through windows or covers. Less light lost is almost always a good thing.
• Refractive Index: Acrylic has a refractive index of approximately 1.49. This is important for lens design and any application where light bending is a factor. It’s relatively close to crown glass (around 1.52), making it a viable, lightweight alternative in many optical systems. This predictability is crucial for engineers designing optical elements.
• Haze: Haze is the cloudiness or scattering of light as it passes through a material. Acrylic typically has very low haze values, often less than 1-2% for optical grades. This contributes to its "crystal clear" appearance and ensures sharp, undistorted vision. For high-quality displays or lenses, low haze is non-negotiable.
• Yellowness Index & UV Stability: A common failure point for some plastics outdoors is yellowing due to UV exposure. Standard PMMA has excellent inherent UV stability. It resists yellowing and maintains its light transmission properties for many years, even in direct sunlight. This is a huge advantage over materials like unstabilized polycarbonate or styrene. We often recommend it for outdoor-facing components for this very reason.

• Clarity & Colorability: In its natural state, PMMA is water-clear. It can also be easily colored to produce a vast range of transparent, translucent, and opaque shades with excellent vibrancy and consistency.	Optical Property	Typical PMMA Value/Characteristic	Benefit for Your Electronic Components, Michael
  Light Transmittance	Up to 92% (visible spectrum)	Brighter displays, efficient light guides, clear viewing.
  Refractive Index	~1.49	Predictable optics, suitable for lens/light pipe design.
  Haze	<1-2% (optical grades)	Crystal clear, sharp image transmission, no distortion.
  UV Stability	Excellent (inherent)	Resists yellowing, maintains clarity and aesthetics long-term.
  Abbe Number	~58	Low chromatic aberration (color fringing) in lenses.

  When you need top-tier optical performance without the weight or fragility of glass, acrylic is very often the answer. Its ability to transmit light so efficiently and clearly, and to maintain that clarity over time, is what sets it apart for so many of the applications we see at CKMOLD. It just makes things look good and perform optically very, very well.

  How Does Acrylic Handle Heat and Cold in Real-World Use?

  Your components might be used in devices that get warm, or they might be shipped through varying climates. So, how does acrylic cope with temperature changes? What are its limits before it starts to soften or become too brittle?

Acrylic has a continuous service temperature of around 70-90°C (160-190°F) depending on the grade. It has a relatively high coefficient of thermal expansion and low thermal conductivity, meaning it expands significantly with heat and is a good insulator.

I remember a project where an acrylic housing was placed too close to a heat-generating component in an electronic device. Over time, we saw slight warping. We worked with the client to improve airflow and add a small heat shield, which solved it. It’s a reminder that while acrylic is decent, you need to be aware of its thermal limits, especially for your electronic enclosures, Michael.
Let’s explore its thermal behavior:

Understanding Acrylic’s Thermal Characteristics

• Heat Deflection Temperature (HDT): This is the temperature at which a standard test bar deflects by a certain amount under a specific load. For general-purpose acrylic, the HDT at 1.8 MPa (264 psi) is typically in the range of 85-105°C (185-221°F). For lower loads (0.45 MPa or 66 psi), it can be higher, around 95-110°C. This gives an indication of its short-term heat resistance.
• Continuous Service Temperature: This is a more practical measure for long-term use. Most standard acrylic grades are recommended for continuous use up to about 70-90°C (160-190°F). Above this, it may start to soften, lose dimensional stability, or degrade over time. Specialty high-heat acrylic grades can push this a bit higher.
• Coefficient of Linear Thermal Expansion (CLTE): Acrylic has a relatively high CLTE, typically around 70-77 x 10⁻⁶ m/(m·°C) (or µm/m°C). This means it expands and contracts quite a bit with temperature changes – more than metals and some other plastics. This is a critical design consideration! You need to allow for this movement if acrylic parts are constrained or assembled with other materials with different expansion rates to avoid warping or stress.
• Thermal Conductivity: Acrylic is a poor conductor of heat, with a thermal conductivity of about 0.17-0.19 W/(m·K). This means it’s a good thermal insulator. This can be beneficial in some applications (e.g., reducing heat transfer), but it also means it can trap heat if it’s enclosing heat-generating components.

• Brittleness at Low Temperatures: While acrylic performs well at room temperature, like many plastics, it can become more brittle at very low temperatures (e.g., below freezing). If your component will see sub-zero conditions, impact resistance will be further reduced.	Thermal Property	Typical PMMA Value Range	Key Takeaway for Your Design Process, Michael
  Heat Deflection Temp. (HDT @1.8MPa)	85-105°C (185-221°F)	Good for short-term exposure to moderate heat.
  Max. Continuous Service Temp.	70-90°C (160-190°F)	Don’t exceed this for long periods to avoid softening/warping.
  Coeff. of Linear Thermal Expansion	~75 x 10⁻⁶ /°C (4.2 x 10⁻⁵ /°F)	Crucial! Allow space for expansion/contraction in assemblies.
  Thermal Conductivity	~0.18 W/(m·K)	Good insulator; can trap heat from internal components.
  Low-Temperature Brittleness	Becomes more brittle below 0°C (32°F)	Consider for applications in very cold environments.

  So, Michael, acrylic is generally fine for most indoor consumer electronics operating temperatures. The main thing to watch out for is that thermal expansion – always design with that in mind, especially for larger parts or those fixed rigidly. And if your device generates significant heat near the acrylic, ensure there’s adequate ventilation or shielding. It’s not a high-temperature superstar, but it’s predictable and manageable within its range.

  Is Acrylic a Reliable Choice for Electrical Insulation?

  In consumer electronics, you often need materials that won’t conduct electricity, preventing shorts and ensuring user safety. How does acrylic perform as an electrical insulator? Is it a safe bet around your circuits?

Yes, acrylic (PMMA) is an excellent electrical insulator, characterized by high dielectric strength and high volume resistivity. This makes it a suitable material for applications requiring electrical insulation near low to moderate voltage components.

We’ve supplied acrylic for various insulating components in electronic assemblies – things like standoffs, barriers, or clear covers over low-voltage PCBs. Its inherent insulating properties are a big plus. It’s not something you’d use for high-voltage power transmission, of course, but for typical electronics, it’s usually more than adequate.
Let’s look at the specifics that make it a good insulator:

Acrylic’s Insulating Capabilities

• Dielectric Strength: This measures a material’s ability to withstand a high voltage before electrical breakdown (arcing) occurs. Acrylic typically has a dielectric strength in the range of 15-20 kV/mm (kilovolts per millimeter) or about 380-500 V/mil. This is quite high and indicates it can effectively prevent current from passing through it under significant electrical stress. For comparison, air is around 3 kV/mm.
• Volume Resistivity: This indicates how strongly a material opposes the flow of electric current through its bulk. Acrylic has a very high volume resistivity, often greater than 10¹⁴ to 10¹⁶ ohm-cm. This means it’s extremely resistant to conducting electricity, making it a superb insulator.
• Surface Resistivity: Similar to volume resistivity, this measures resistance to current flow across the surface of the material. Acrylic also exhibits high surface resistivity, again contributing to its excellent insulating properties.
• Dielectric Constant (Permittivity): At typical power frequencies (e.g., 60 Hz to 1 MHz), acrylic has a dielectric constant of around 2.5 to 3.7. A lower dielectric constant is generally better for high-frequency insulation as it reduces capacitive losses. While not as low as some specialized materials like PTFE (Teflon), it’s good for many general-purpose insulating tasks.

• Dissipation Factor (Loss Tangent): This represents the energy lost as heat when the material is subjected to an alternating electric field. Acrylic has a relatively low dissipation factor (e.g., 0.02-0.05 at 1 MHz), meaning it doesn’t waste much energy as heat in AC applications, which is good.	Electrical Property	Typical PMMA Value Range	Significance for Electronic Housings/Components, Michael
  Dielectric Strength	15-20 kV/mm (380-500 V/mil)	Excellent ability to prevent electrical breakdown.
  Volume Resistivity	>10¹⁴ – 10¹⁶ ohm-cm	Extremely high resistance to current flow.
  Surface Resistivity	>10¹⁴ – 10¹⁵ ohm/square	Prevents current leakage across the surface.
  Dielectric Constant @1MHz	~2.7 – 3.5	Good for general insulation; low enough for many apps.
  Dissipation Factor @1MHz	~0.02 – 0.05	Low energy loss in AC fields, efficient insulation.

  So, Michael, when you need a clear material that also needs to provide good electrical insulation for the voltages typically found in consumer electronics, acrylic is a very solid choice. It helps keep things safe and prevents unwanted electrical pathways. Just ensure designs account for creepage and clearance distances appropriate for the voltages involved, as with any insulator. But fundamentally, acrylic’s electrical properties are on your side.

  Conclusion

  Acrylic PMMA offers a fantastic blend of optical brilliance, good mechanicals (especially hardness), and reliable thermal and electrical properties, making it a go-to for many engineering designs, especially in consumer electronics. Understanding these details helps!