Fibreglass Matting CSM - 300g , 450g & 600g Sent Rolled -Various size options. This fibreglass matting is often called CHOPPED STRAND MATT ( CSM ). Its mostly used together with Fibreglass ( polyester ) resin. The matting provides the strength and structural support with the resin acting as a binder. From the drop down menu, you can select 3 different " weights " or thickness. This is measured in "grams per sq M". The 600g/ m has twice the amount of glass strands compared with the 300g option with the 450g taking the middle ground. The heavier material will be stiffer and less pliable, If you have curves and complex shapes, consider using the lighter glass and building up layers ( 2 layers of 300g/m for example ).