Short answer: Clear acrylic (PMMA) sheet has a density of 1.19 g/cm³, a refractive index of 1.49, about 92% light transmission, a tensile strength near 10,000 psi (69 MPa), and a flexural modulus around 450,000 to 490,000 psi (3.1 to 3.4 GPa). Cast sheet softens a little higher than extruded (Vicat about 239 °F vs 220 °F) and is rated for continuous service up to about 180 °F (82 °C), against about 160 to 190 °F for extruded. Both are combustible, rated UL 94 HB.
Key facts
- Density: 1.19 g/cm³ (about 0.043 lb/in³), roughly half the weight of glass.
- Optics: refractive index 1.49; clear sheet transmits about 92% of visible light.
- Strength: tensile about 10,000 to 11,000 psi; flexural about 16,000 to 17,000 psi.
- Heat: deflects under load at about 195 to 210 °F; maximum continuous use about 160 to 180 °F for most grades.
- Fire: combustible, UL 94 HB (slow horizontal burning), not self-extinguishing.
- Electrical: a good insulator, about 430 V/mil (17 kV/mm) dielectric strength.
Acrylic sheet properties table
Typical values for general-purpose clear sheet, about 1/4 in. (6 mm) thick unless noted, at room temperature. "Cast" values come from the ACRYLITE cell cast (GP) and Plexiglas G data sheets; "extruded" from ACRYLITE premium (FF) and Plaskolite OPTIX. Where two makers report different numbers, both are shown. Typical values are not specification minimums.
| Property (test) | Cast acrylic | Extruded acrylic | Data sheet |
|---|---|---|---|
| Specific gravity (ASTM D792) | 1.19 | 1.19 | ACRYLITE GP, ACRYLITE FF, OPTIX |
| Refractive index (ASTM D542) | 1.49 | 1.49 | ACRYLITE GP, Plexiglas G, OPTIX |
| Light transmission, total (ASTM D1003) | 92% | 92% | ACRYLITE GP, ACRYLITE FF, OPTIX |
| Haze (ASTM D1003) | under 1% (GP); under 2% (Plexiglas G) | 2% (OPTIX) | ACRYLITE GP, Plexiglas G, OPTIX |
| Tensile strength (ASTM D638) | 10,000 psi (69 MPa) GP; 10,500 psi Plexiglas G | 10,000 psi (69 MPa) FF; 11,030 psi OPTIX | ACRYLITE GP, Plexiglas G, ACRYLITE FF, OPTIX |
| Tensile modulus (ASTM D638) | 400,000 psi (2,800 MPa) GP; 450,000 psi Plexiglas G | 400,000 psi FF; 490,000 psi OPTIX | Same four |
| Elongation at break (ASTM D638) | 4.2% GP; 4.9% Plexiglas G | 4.5% FF; 5.8% OPTIX | Same four |
| Flexural strength (ASTM D790) | 16,500 psi (114 MPa) GP; 16,000 psi Plexiglas G | 17,000 psi (117 MPa) | ACRYLITE GP, Plexiglas G, ACRYLITE FF, OPTIX |
| Flexural modulus (ASTM D790) | 475,000 psi (3,300 MPa) GP; 450,000 psi Plexiglas G | 480,000 psi FF; 490,000 psi OPTIX | Same four |
| Compressive strength, yield (ASTM D695) | 18,000 psi (124 MPa) | 17,000 psi (117 MPa) | ACRYLITE GP, ACRYLITE FF |
| Izod impact, notched (ASTM D256) | 0.4 ft-lb/in. (21.6 J/m) GP; 0.3 Plexiglas G | 0.4 ft-lb/in. FF; 0.28 to 0.4 OPTIX | Same four |
| Rockwell hardness (ASTM D785) | M-94 GP; M-100 Plexiglas G | M-93 FF; M-95 OPTIX | Same four |
| Deflection temperature at 264 psi (ASTM D648) | 210 °F (99 °C) GP; 205 °F Plexiglas G | 195 °F (91 °C) FF; 203 °F OPTIX | Same four |
| Vicat softening point (ASTM D1525) | 239 °F (115 °C) | 220 °F (105 °C) | ACRYLITE GP, ACRYLITE FF |
| Maximum recommended continuous service | 180 °F (82 °C) GP; 180 to 200 °F Plexiglas G | 160 °F (71 °C) FF; 170 to 190 °F OPTIX | Same four |
| Forming temperature | 340 to 380 °F (170 to 190 °C) GP; 290 to 360 °F Plexiglas G | about 300 °F (149 °C) FF | ACRYLITE GP, Plexiglas G, ACRYLITE FF |
| Coefficient of thermal expansion (ASTM D696) | 0.000040 in./in./°F (7.2 × 10⁻⁵ /°C) GP; 3.9 × 10⁻⁵ /°F Plexiglas G | 0.000040 in./in./°F FF; 3.0 × 10⁻⁵ /°F OPTIX | Same four |
| Thermal conductivity (k-factor) | 1.3 BTU·in./(hr·ft²·°F) (0.19 W/m·K) | 1.3 BTU·in./(hr·ft²·°F) (0.19 W/m·K) | ACRYLITE GP, ACRYLITE FF |
| Specific heat at 77 °F | 0.35 BTU/(lb·°F) (1,470 J/kg·K) | 0.35 BTU/(lb·°F) | ACRYLITE GP, ACRYLITE FF |
| Water absorption, 24 hr (ASTM D570) | 0.2% | 0.2% FF; 0.4% OPTIX | ACRYLITE GP, ACRYLITE FF, OPTIX |
| Dielectric strength, short time (ASTM D149) | 430 V/mil (17 kV/mm) | 430 V/mil (17 kV/mm) | ACRYLITE GP, ACRYLITE FF |
| Dielectric constant, 60 Hz (ASTM D150) | 3.5 | 3.6 | ACRYLITE GP, ACRYLITE FF |
| Volume resistivity (ASTM D257) | 1.6 × 10¹⁶ ohm·cm | 10¹⁶ ohm·cm | ACRYLITE GP, ACRYLITE FF |
| Horizontal burning rate (ASTM D635) | 1.2 in./min at 3 mm (GP); under 1.0 in./min (Plexiglas G) | 1.0 in./min at 1/8 in. (FF); 1.019 in./min (OPTIX) | Same four |
| Flammability classification (UL 94) | 94 HB | 94 HB | Plexiglas G, OPTIX |
| Self-ignition temperature (ASTM D1929) | 910 °F (490 °C) GP; 860 °F Plexiglas G | 850 °F (455 °C) FF; 833 °F OPTIX | Same four |
| Residual shrinkage on heating (ASTM D702) | 2% max | up to 3% in the extrusion direction (1/8 in. and thicker) | ACRYLITE GP, ACRYLITE FF |
| Sound transmission class (STC) | not listed separately (sound loss follows weight, so expect similar values) | 23 at 3 mm, 28 at 6 mm (ACRYLITE); 27 (OPTIX) | ACRYLITE glazing, OPTIX |
Where cast and extruded acrylic really differ
Most of the table is the same plastic with the same numbers. The real differences come from how the sheet is made. Cast sheet has much longer polymer chains, so it softens at a slightly higher temperature, resists solvents and crazing better, and engraves frosty white. Extruded sheet is pushed through a die, which locks in some orientation, so it shrinks more in one direction when heated and is more sensitive to solvent cement. Extruded is also more uniform in thickness. For the practical side, see cast vs extruded acrylic.
How do these numbers translate to real parts?
- Strength: short-term tensile strength isn't a design load. ACRYLITE advises keeping continuous loads under about 1,500 psi to avoid crazing. See how strong acrylic is.
- Heat: the 160 to 180 °F service limit matters more than the melting range. See acrylic heat resistance.
- Expansion: 0.00004 in./in./°F means a 48 in. panel moves about 0.2 in. over a 100 °F swing. Plan clearances with the thermal expansion calculator.
- Weight: 1.19 g/cm³ makes 1/4 in. (6 mm) sheet about 1.46 lb/ft². The weight calculator does any size.
- Moisture: 0.2% absorption sounds tiny but is enough to bow a lid over a fish tank. See does acrylic absorb water.
Need parts cut from cast or extruded sheet? Pick either in the instant quote and see the price as you go.
Questions
What is the density of acrylic?
1.19 g/cm³ (specific gravity 1.19, about 0.043 lb/in³) for both cast and extruded clear sheet. Colored and impact-modified grades can differ slightly.
What is the refractive index of acrylic?
About 1.49 (ASTM D542, sodium D line at 73 °F). Glass is about 1.5 and polycarbonate about 1.586, which is why acrylic and glass look so alike.
Does acrylic have a melting point?
Not a sharp one. It softens through a range: deflection under load near 195 to 210 °F, forming around 290 to 380 °F depending on grade, and Plaskolite lists 300 to 315 °F as a melting range for extruded OPTIX.