Currently there are three categories of geogrids available:
The first, and ‘original’, geogrids are commonly referred to as ‘punched and drawn’ geogrids.
A sheet of either HDPE or Polypropylene has holes punched into it in a regular pattern and the sheet is then ‘drawn’ or ‘stretched’ into the finished product. The drawing is done under controlled conditions of temperature and strain rates to avoid fracture whilst allowing ductile flow of the molecular chains. This operation aligns the molecular chains in the direction of drawing to convert low-strength polymer into high-strength grids.
The second category of Geogrids is ‘coated yarn’ types. They are, in fact, technical textiles in the form of grids and use bundles of fibres (most commonly Polyester) as the reinforcing component that are then coated to provide protection during installation and in service. The grid structure is formed by knitting or intertwining the transverse and longitudinal bundles of fibres.
The third category of Geogrids is made by laser or ultrasonically welding together polyester or polypropylene rods or straps (as used in packaging/shipping) in a gridlike pattern.