Polycarbonate Sheet, Optical Grade

Optical-grade polycarbonate sheet is polished, UV-stabilised transparent stock for applications where the optics have to be better than general-purpose sheet can manage - face shields, instrument and gauge covers, vehicle and equipment windscreens, and laminating stock. Light transmission is published at 88% for clear on the current datasheet, with specific gravity 1.20.

Mechanical and thermal properties are those of general-purpose polycarbonate: tensile 9,500 psi ultimate and 9,000 at yield on a 340,000 psi modulus with 110% elongation, flexural 13,500 psi on 345,000, compressive 12,500 psi, Rockwell M70 and R118, heat deflection 270F at 264 psi and 280F at 66 psi, water absorption 0.15%. The optical selection buys surface and clarity, not strength.

Temperature, stated honestly. Heat deflection temperature is 270F at 264 psi and 280F at 66 psi by ASTM D648, but that is a short-duration softening test and must not be used as a service limit. Published maximum continuous service temperature in air is 240 to 250F depending on the publisher, with intermittent exposure to 275F published. Parts under sustained load should be derated well below that, and anything load-bearing near the top of the range needs creep data.

One thing to check before you order, and this is distributor practice rather than anything a manufacturer prints. Polycarbonate sheet sold as "1/4 inch" is commonly 0.220 inch, which is the 5.6 mm North American extruded gauge, or 0.236 inch, which is the metric 6 mm gauge - not 0.250 inch. Those are 7% apart in thickness and in weight, and the difference matters wherever the sheet has to fit a frame, a channel or a glazing pocket. The thickness on each listing here is the actual decimal, not the nominal label.

Chemical compatibility and cleaning, which is where most polycarbonate failures start. Clean it with mild diluted dish soap and a soft microfibre cloth, or an ammonia-free glass cleaner. Do NOT use ammoniated glass cleaner - the common blue kind - because ammonia attacks polycarbonate, and the resin maker's own testing shows 0.1% ammonia is enough to do damage in the presence of water. Also avoid abrasive or high-alkaline cleaners, scrapers and squeegees, dry rubbing, and solvent in direct sun. Isopropyl alcohol diluted 50/50 with water handles oil and tar. Acetone, MEK, methylene chloride, chloroform, toluene, xylene and aromatic fuels all attack it, and so do amines and the plasticisers that migrate out of flexible PVC - which is why PVC gasket, tape and cable tie contact is a real failure mode. The important subtlety is that chemical resistance is not a fixed property: stress cracking only develops where the part is in tension, so a cold-bent, over-torqued or tightly framed part will fail with chemicals a compatibility chart calls safe.