Geotextile AOS Property – We know it’s confusing, but it doesn’t have to be!

AOS (Apparent Opening Size) is a property that is commonly tested on a variety of geotextile fabrics.

AOS is usually reported in two units of measurement on a geotextile datasheet:

  1. English US Sieve
  2. Metric Units (mm)

Here is the confusing part…
When the test results are reported in English US Sieve units, the result is a MAXIMUM, meaning that the result needs to be equal to or lower than what is required by an engineer. However, when reported in Metric Units (mm) the test results are reported are the SMALLEST (minimum) allowable opening.

These units are always reported side by side on a datasheet, which can look confusing because the smaller the US Sieve number is, the larger the equivalent Metric Unit (mm) number becomes! Check out this chart showing which results in English US Sieve are equal to which result reported in a Metric Unit (mm):

How can we avoid this confusion?
Well, it would be terrific if the industry wide standard would be to use ONLY the metric units! But we can’t change that (can you?) so it is probably best to gain an understanding of the two units of measurement and how they equate to one another, and keep this chart handy!

Would you like to see how the test is performed? We think it’s really fascinating! Shout-out to GSI for the fantastic video:

Did you know Carthage Mills has been in the geosynthetics industry for over 60 years? That’s longer than any other company in the nation! Connect with an industry expert today for more information about all-things geosynthetic!