How is Glass Tested?

How is Glass Tested?

How is Glass Tested?

At Kensington Glass Arts Inc. (KGa), we care about ensuring our customers are aware of how we measure the quality of glass. There are various tests that one can conduct to measure not only the overall quality, but the glass’s ability to block sound, and how well the glass is at conducting heat and heat flow. To find out what measurements and tests are conducted on glass, keep reading this blog article.

Visual Test

The first test that is performed on glass is usually a visual test. Anyone, glazier or not, can perform a visual test. However, there are standards for visual tests set out by ASTM International for performing visual tests for glass. ASTM International has documented standards for how to measure and calculate the quality of things, including glass. Each type of glass has its own standards for evaluation. In general, a good test to see if a piece of glass has defects is as follows:

  • Stand 10 feet back from the glass
  • Face the front of the glass at a 90-degree angle
  • View in daylight, but not direct sunlight
  • Inspect the central 80% portion of the glass.

Generally, if you cannot see a defect from this test, then the glass has no defects. The reason for these standards is because glass is meant to be looked through, not looked at. It’s rare to look directly at the glass up-close in practical usage. Therefore, issues on the glass not readily visible during the ATSM test then they are not considered true defects.


Another way that glass is measured is through how much sound passes through it. STC, or the Sound Transmission Coefficient, refers to how well an object blocks or reduces noise. This is measured with a rating scale, where a higher number indicates a higher ability to diminish sound. For your typical interior office tempered glass wall partitions, you can expect an STC of about 32. Meanwhile, laminated glass has a slightly higher STC at 34. This is because the multiple layers deform the sound waves in different ways, muffling the sound even further than a monolithic piece of glass. If the layers of glass are mixed in size, such as a 1/2″ piece with a 3/4″ piece, the sound is even further muffled. This is because the different sizes mix the sound with different effects. Insulated glass units (IGU’s) are typically thinner than laminate or tempered glass, however, the airspace between the panes of glass causes the sound to be even further muffled.

U-Value and R-Value

U-Value, or U-Factor, is best described as the measure of heat loss in glass due to a difference in exterior and interior temperatures. The lower the U-Value, the better the glass is at insulating heat. U-Value is calculated by a mathematical formula that measures the rate of how heat flows through 1 square foot of material. U-Value is an important value to determine how energy efficient your windows are, especially during the wintertime.

Meanwhile, the R-Value is the resistance of glass to heat flow. While a lower U-Value means better insulation, the opposite is true for the R-Value. The larger the R-Value, the better at insulating. Similar to U-Value, R-Value is calculated by a mathematical formula.

About Kensington Glass Arts, Inc.

Kensington Glass Arts, Inc. (KGa) is a commercial glass fabricator, installer, and commercial service provider. Our process-driven approach and ISO 9001 certification support our quality-focused throughout with on-time delivery to exacting standards and details. In addition, our North American Contractor Certification (NACC) and certification from the Safety Glazing Certification Council (SGCC) ensure our glass is made with documented quality standards. From nationally recognized museums to law firms, and corporate headquarters, Kensington Glass Arts can handle all your glass installation and fabrication needs. To learn more about our products and services, visit our Contact Us page to give us a call.