Glass vs. Acrylic: a Comparision

Glass needs to be very thick and has usually one or more laminated layers to be able to bear water pressure. It has a greenish tint. Plexiglas / Acrylic is optically superior and has no visible tint

shattered iphone glass

impact test for spherical acrylic window with a 560kg impact mass. curtessey of J.Stachiw

Plexiglas is often chosen as an replacement material to mineral glass (also called flat glass, Borosilicate glass or Echtglas in German). Plexiglas© (which is a brand name for acrylic) and mineral glass are both transparent building materials. Differences in the properties of the two materials include:
  • Acrylic glass transmits more light than glass. Up to 92% of visible light is transmitted through acrylic. Mineral glass transmits 80-90%, depending on type of glass and manufacturer. This is especially relevant, when comparing load bearing transparent materials. These windows are mostly several centimeters thickLoad bearing mineral glass that we know of is derived from bullet-proof glass – in relation to acrylic it appears milky. Update Sept.8 2014: One of our clients informed me about a laminated glass called Optiwhite. This laminated glas has a reduced iron oxide components. Its optical quality is less tinted. Optiwhite glazing can withstand pressures of up to 1m (1000mm water level over window bottom). This means that Optiwhite is only suitable for very small, shallow underwater windows.
  • UV Resistance / Aging: Using glazing outdoors exposes the material to potentially high amounts of ultraviolet light (UV). It is a common misconception that UV leads to yellowing of acrylic glazing. As this is true for some brands and manufacturers, it is not true for Plexiglas and other brands we use. In fact we give 30 years warranty against yellowing. Safety glas consists of multiple layers of mineral glazing, seperated by plastic laminate. When safety glas is used for open top swimming pool glazing , the top is exposed to direct sunlight. This does lead to yellowing as is admitted by safety glas manufacturers.
  • Heat Insulation: The value of Thermal Conductivity is much higher for acrylic than for laminated glazing. For most types of acrylic is 0.19 W/mK. This means: no condensation on the acrylic window and few heat loss. Double glazing on the other hand is a much better insulator than even thick acrylic windows. But double glazing can not be used under water, so this argument does not really count for us.
  • Acrylic can be easily processed – quite similar to wood.
  • The surface of acrylic is softer and more easily scratched than mineral glass. It is advised to check acrylic cleaning guidelines in order to prevent abrasive or chemical dammage. However, it is easy to polish acrylic in order to remove blemishes. Scuffed mineral glass would need to be replaced.
  • Acrylic glass is less dense – its density can range from 1150-1190 kg/m3. This is less than half the density of glass which ranges 2400 to 2800 kg/m3. Transportation and assembling of acrylic building materials are consequently easier and cheaper.
  • Acrylic glass has a higher impact strength than glass and will not shatter. Shattering is wanted by most applications where tempered (tough-ended) glass is used, e.g in automobiles. However it is not wanted for most others. Non-shattering makes Acrylic the ideal material for applications where it would induce fatal losses, like in submarine windows. Hydrosight Underwater Windows are made of acrylic. As acrylic doesn’t shatter it is an easy material to transport. No special precautions need to be made to ensure a save arrival at the site of installation. Moving the window is easy and safe. Moving mineral glass might need security measures depending on local law. Polycarbonate is also a great material that does not shatter.
  • Glas is considered to be cheaper than acrylic. This assumption probably originates in the small aquarium market. Small aquariums are usually made of float glass. Only more expensive models use acrylic glazing. Why is this so? Small aquariums are made in high quantities. The aquarium makers can order large number of same size glazing. If you want an individually configured and sized aquarium, you might be cheaper using acrylic. Here is an example: A round window, clear view diameter 80cm, rated for 5m water column, using laminated glass: 3500EUR; A round window, clear view diameter 80cm, rated for 5m water column, using casted acrylic: 900EUR (please note price are for comparison only. They originate from our internal price analysis in 2016).
While there are benefits to both Plexiglas and mineral glass viewing panels depending on the application, in recent years, acrylic has surpassed mineral glass in versatility and multiple uses. The use of glass in underwater technology is declining.

Categories: Technology of Glazing under Pressure
Created: 22 March 2013
Last Modified: 7 March 2017

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