Does acrylic insulate?

Key facts

• Thermal conductivity: 0.19 W/m·K (1.3 BTU·in./hr·ft²·°F) for ACRYLITE cast and extruded.
• Single pane vs glass: U-factor about 10% lower than glass of equal thickness (ACRYLITE); Plaskolite says glass conducts heat about 4 times faster than OPTIX-L.
• Single-glazed U-factors (winter, ACRYLITE): 1.06 at 3 mm, 1.02 at 4.5 mm, 0.97 at 6 mm, 0.89 at 9 mm, 0.58 at 31.5 mm (BTU/hr·ft²·°F).
• Double glazed (winter, Plaskolite OPTIX-L): about 0.49 to 0.55 with a 1/4 in. air space and 0.43 to 0.47 with a 1/2 in. air space, roughly half of single glazing.
• Interior storm windows: 6.5 to 10% heating and 3.5 to 5% cooling savings in typical use (ACEEE, citing DOE-funded research).

Is acrylic a better insulator than glass?

Slightly. Acrylic's thermal conductivity is several times lower than glass's, but for a single thin pane, most of the resistance to heat flow is in the thin films of still air on each surface, not in the pane itself. That's why the U-factor of single-pane acrylic is only about 10% better than glass of the same thickness, according to ACRYLITE. A 1/4 in. acrylic pane at about 0.97 BTU/hr·ft²·°F still loses heat fast. What acrylic does have is a warmer surface than glass, which helps reduce condensation, and it resists thermal shock better than glass.

How much do acrylic window inserts help?

A lot more than the sheet alone suggests, because they add a second pane and trap still air. Plaskolite's OPTIX-L guide gives winter U-factors of 1.06, 1.03, and 0.96 for single-glazed 1/8, 3/16, and 1/4 in. sheet, against 0.55, 0.52, and 0.49 when double glazed with a 1/4 in. air space, and 0.47, 0.45, and 0.43 with a 1/2 in. air space. Interior storm panels also cut air leakage, which is often where old windows lose the most. ACEEE, summarizing DOE-funded research and the AERC rating program, puts typical savings from interior storm windows at about 6.5 to 10% of heating energy and 3.5 to 5% of cooling energy.

PNNL's Building America guide notes that plastic interior panels are lighter, flexible, impact resistant, and easy to remove, usually held by a gasket-style friction frame or magnets. They can earn an AERC rating but not ENERGY STAR, which requires low-E coated glass. Low-E glass storm windows save more energy, so if maximum savings is the goal and the panel can be heavier and fixed, consider low-E glass.

How to make an acrylic interior storm panel work

1. Seal the edges. The air gap only insulates if it's still air. Use a compressible gasket or foam tape all around.
2. Use 1/8 in. for small windows, 3/16 to 1/4 in. for large ones, so the panel doesn't bow; thicker also blocks more sound.
3. Leave clearance for expansion: the sun-facing pane moves with temperature. See how to measure for acrylic cut to size.
4. Make it removable with magnets, a friction frame, or turn buttons so you can clean both surfaces.
5. Watch for condensation between panes. PNNL notes that if the storm panel isn't airtight, moist room air can condense on the cold original glass. Seal the panel better first, and reduce indoor humidity.

We cut insert panels to size from clear, UV-filtering, or non-glare acrylic; price yours in the instant quote, or read about acrylic window inserts.

Does acrylic insulate greenhouses and skylights?

Single-pane acrylic on a greenhouse behaves like single glass, slightly better. Twin-wall (multiwall) sheet traps air in its channels and insulates far better, which is why it's common on greenhouses. Thick cast acrylic insulates better simply because it's thick: ACRYLITE's 31.5 mm (1.25 in.) sheet has a winter U-factor of 0.58. See acrylic greenhouse panels.

Questions

Sources

• ACRYLITE: Cell cast sheet (GP) physical properties (U-factors)
• Plaskolite: OPTIX-L continuous cast acrylic sheet fabrication guide (Table IX)
• PNNL Building America Solution Center: Interior storm windows and panels
• ACEEE: Residential window attachments