If they were all the same thickness, a small rock could break a sheet of glass, a hammer could break acrylic, and — unless it was swung by Thor — the hammer would bounce off a sheet of polycarbonate.
In Coastal Florida, hurricanes with winds up to 150 mph are a part of life. From paper clips and spoons to trees and cars, anything scooped up by those winds become projectiles moving at that same speed.
In Florida, there is a hurricane-rating test that fires 2×4 pieces of lumber out of a cannon at hurricane speeds into windows and skylight domes at point-blank range.
When it comes to impact resistance, polycarbonate is far superior to acrylic — or anything else.
Shape, Thickness and the Nuisance of Moisture
The question then becomes thickness. For domes with small surface areas, such as those that protect security cameras, very thin layers can hold up. But the larger the dome is built, the thicker the polycarbonate must be.
The shape of the dome also comes into play.
The structural benefit to being rounded and curved is that objects tend to glance off instead of crashing straight on, as they would with a flat surface.
But it comes with manufacturing challenges. A hygroscopic material, polycarbonate naturally attracts and absorbs a tremendous amount of moisture, literally sucking water out of the surrounding air.
When forming, polycarbonate sheet needs to be heated far above the boiling point of water. When you do so, air bubbles form from water vapor inside unless you take great care to dry the sheet prior to forming. For example, six millimeter thick polycarbonate must be baked in an oven for between 12 and 24 hours before thermoforming.
When it comes to plastic dome manufacturing, acrylic is easier to work with because it doesn’t make bubbles, it doesn’t need to be dried, and it has better light stability.
But whether it’s a plastic dome protecting children on playground equipment at McDonald’s or skylights in buildings that have to stand up to category 5 hurricanes in South Florida, polycarbonate is the choice when breakability is not an option.