What is pore size?

Pore size is a measurement of the gaps between the fibres within a permeable material such as a geotextile.  TERRAM nonwoven geotextiles consist of a tangled web of randomly orientated polypropylene fibres, which result in a wide range of different size pores (gaps) ideal for filtering soil particles of different sizes, (gravels, sands and course silts) yet allowing the passage of water. Samples are tested in a laboratory to determine the range of pore sizes.  To allow comparison between different geotextiles the apparent opening size (AOS) value is declared. The AOS is where 90% of the geotextile sample pores are of the same or smaller size (O90 value). The typical pore size allows designers to determine the suitability of a particular geotextile for filtering different grades of soil materials.