What is Perspex? What is the difference between Polycarbonate and Acrylic sheet and Glass?

Many customers visit our showroom with these questions: what is Perspex sheet? What is the difference between Perspex sheet, acrylic sheet, and polycarbonate sheet? To assist you in making an informed decision for your project, we'll provide a detailed explanation of these plastic materials.

Perspex is a brand name for acrylic sheeting. Also known as PMMA, it is a type of transparent thermoplastic known for its clarity, lightweight nature, and versatility. The term "Perspex sheet" is often used in Melbourne, Australia and some other regions to refer to acrylic sheets, similar to how "plexiglass sheet" is used in the United States.

Now, let's discuss the differences between polycarbonate, acrylic sheet, Perspex, and glass.

1. Material Composition

• Acrylic Sheet (Perspex): Also known as PMMA, acrylic is a thermoplastic derived from acrylic acid. Available as extruded or cast acrylic sheet, it is known for its glass-like clarity and ease of fabrication. Acrylic panels are generally harder and more brittle compared to polycarbonate.
• Polycarbonate Sheet: Polycarbonate is another thermoplastic, derived from carbonate groups. Most polycarbonate sheet is extruded. It is known for its exceptional impact resistance — 250 times stronger than glass and 30 times stronger than acrylic — making it suitable for applications where durability is crucial. Polycarbonate sheeting is more flexible and impact-resistant.
  
• Glass: Glass is a hard, brittle, and transparent material primarily composed of silica (sand), soda ash, and limestone.

2. Clarity

• Acrylic Sheet (Perspex): Acrylic sheets generally have excellent optical clarity of 90–93%, allowing for clear visibility through the material.
• Polycarbonate Sheet: While polycarbonate also offers good clarity of 88–90%, it may not be as optically clear as acrylic. Over time, polycarbonate sheets may be prone to scratching, which can affect clarity.
• Glass: Glass provides high optical clarity, achieving up to 95%, and does not scratch easily.
  

3. Impact Resistance

• Acrylic Sheet (Perspex): Acrylic is more brittle than polycarbonate and less impact-resistant. It is approximately 30 times stronger than glass.
• Polycarbonate Sheet: Polycarbonate is known for its high impact resistance — virtually unbreakable and 250 times stronger than glass. It can withstand significant impacts without cracking or breaking.
  
• Glass: Glass is the hardest but also brittle and can shatter upon impact. Tempered glass has a 0.3–3% self-explosion rate.

4. Weight

• Acrylic Sheet (PMMA): Acrylic is lighter than glass, making it easier to handle and install. Density: 1.19 kg/m² per mm.
• Polycarbonate: Polycarbonate is also lightweight but slightly heavier than acrylic. Density: 1.2 kg/m² per mm.
• Glass: Glass is heavier and denser than both acrylic and polycarbonate at approximately 5 kg/m² per mm.
  

5. Fabrication and Plastic Machining

• Cutting Acrylic Sheet: Acrylic can typically be cut using standard CNC cutting tools designed for plastics. Laser cutting is also a common method due to its precision and clean edges.
  
• Cutting Polycarbonate Sheet: Polycarbonate, being more flexible and heat-sensitive, may require specialised CNC cutting tools or processes to prevent melting or warping. Waterjet cutting or a specialised CNC router with appropriate cooling mechanisms can be effective.
  
• Glass: Glass fabrication involves cutting, grinding, and tempering, and is more rigid and challenging to shape compared to plastics.
• Cutting Speed and Feed Rates:
  • Acrylic generally allows for faster cutting speeds and higher feed rates due to its hardness and brittleness.
  • Polycarbonate may require slower cutting speeds and lower feed rates to prevent overheating and maintain cutting precision.
• Cooling and Chip Removal:
  • Acrylic produces chips and swarf during cutting, which can be removed easily.
  • Polycarbonate generates more heat during cutting, requiring adequate cooling to prevent melting. Chip removal may be more challenging due to the tendency of melted material to adhere to the cutting tool.
• Edge Finish:
  • Acrylic typically produces clean, smooth edges when cut, especially with laser cutting. Acrylic sheet can easily achieve a glossy polished edge by flame polishing or buff polishing.
    
  • Polycarbonate edges may exhibit some melting or roughness. Polycarbonate does not allow for such easy polishing and will not give as clear an edge.
• Bending Differences:
  1. Bending Temperature: Acrylic typically requires 150–180°C. Polycarbonate requires 150–200°C. See our blog on bending polycarbonate sheet.
  2. Bending Methods: Acrylic can be bent using line bending, oven bending, or cold bending with heat. Polycarbonate is often bent using strip heating, oven bending, or a hot air gun, but requires careful temperature control to prevent distortion.
  3. Bending Radius: Acrylic requires a larger bending radius to prevent cracking. Polycarbonate can be bent to tighter radii without damage, making it more suitable for complex shapes.
  4. Surface Finish: Acrylic tends to produce smoother and clearer bent surfaces. Polycarbonate may show some surface imperfections or waviness after bending.
  5. Post-Bending Stability: Acrylic retains its shape well after bending. Polycarbonate may experience some spring-back, requiring additional time or fixtures to hold the desired shape during cooling.

6. UV Resistance

• Acrylic Sheet: Acrylic sheets do not have built-in UV protection by default and may yellow, become brittle, or degrade with prolonged UV exposure. Manufacturers often apply UV-stabilising coatings or additives during production. UV-coated acrylic sheets are commonly referred to as UV-resistant or UV-protected acrylic.
• Polycarbonate Sheet: Many polycarbonate sheets come with built-in UV protection applied during the extrusion process. This UV coating helps block UV rays, prevent yellowing, and extend the lifespan of the sheet. UV-protected polycarbonate is labelled as "UV-resistant" or "UV-coated."
• Glass: Glass is naturally UV-resistant.

7. Fire Grade

Polycarbonate Sheets:

• Polycarbonate is self-extinguishing or flame retardant, meaning it resists or slows the spread of flames. Polycarbonate can be engineered to higher fire grades.

Acrylic Sheet (PMMA):

• The fire rating of acrylic depends on the specific formulation and additives used. Acrylic is generally considered less heat-resistant and less fire-resistant than polycarbonate.
  

Glass:

• Traditional glass is not combustible and does not contribute to the spread of flames. Fire-resistant glass is available for specialist applications.
  

8. Working Temperature

The working temperature of acrylic, polycarbonate, and glass can vary. Here are general guidelines:

Acrylic (PMMA):

• Working temperature range: approximately −40°C to 80°C.
• Acrylic starts to soften and lose mechanical properties at higher temperatures, so prolonged exposure near its upper limit should be avoided.

Polycarbonate:

• Broader working temperature range: approximately −40°C to 120°C.
• Polycarbonate has better high-temperature resistance than acrylic and maintains its impact strength at lower temperatures.

Glass:

• Glass has a high working temperature range and can withstand much higher temperatures than acrylic and polycarbonate.
• Glass does not have a specific melting point but begins to soften at extremely high temperatures well above typical ambient conditions.

9. Cost

The cost of acrylic, polycarbonate, and glass can vary based on thickness, size, quality, and additional features or treatments.

Acrylic Sheet (PMMA):

• Generally more affordable than polycarbonate and glass.
• Cost range: approximately $20–$150 per square metre, depending on thickness and brand.
• Cost may vary based on whether the acrylic is standard, impact-resistant, UV-resistant, or has other special features.

Polycarbonate Sheet:

• Tends to be more expensive than acrylic but offers higher impact resistance.
• Cost range: approximately $30–$200 per square metre.
• Factors such as thickness, UV protection, and multiwall construction can influence the price.

Glass:

• Typically more expensive than both acrylic and polycarbonate.
• Cost range: approximately $50–$500+ per square metre, depending on type (float, tempered, laminated), thickness, and treatments.
• Specialty glass such as low-iron or fire-resistant glass may have higher costs.
  

10. Applications

• Acrylic Sheet: Commonly used for displays, signage, protective barriers, and DIY projects — mainly indoor applications.
• Polycarbonate Sheet: Ideal for applications requiring high impact resistance, such as safety glazing, bulletproof windows, and outdoor structures like pergola roofing, skylights, awnings, polycarbonate cladding, and polycarbonate facades.
  
• Glass: Widely used in windows, doors, mirrors, and architectural applications.

11. Colour Selection

Polycarbonate sheets have a limited colour selection, while Perspex (acrylic) sheet is available in a wide variety of colours.

In summary, while acrylic sheet (Perspex) and polycarbonate share some characteristics as transparent thermoplastics, they have distinct differences in terms of impact resistance, clarity, and applications. The choice between them depends on the specific requirements of your project.