Waterproofing can be done through two processes:
Impregnated Waterproof Fabrics - Kiwi Camping's Choice
This process involves waterproofing by impregnating each fibre usually through a specially controlled immersion process. The usual water head rating is from 450-750mm.
This method has more advantages as impregnating allows the pores of the fabric to breathe naturally, avoiding condensation. The fibres in the fabric have the ability to move back around the stitch hole to prevent seam leakage, the most common fault in any tent!
Coated Waterproof Fabrics
Spread coating can be likened to a coat of paint being spread onto the fabric. Most coated fabrics will have a water head rating of between 1000-1600mm. Although this method produces a higher waterproofing rating, the spread coating seals the pores in the fabric and will not allow it to breathe. Once the coating is punctured by sewing, the fabric cannot shrink easily around the stitch holes and this makes the tent less waterproof.
Superior waterproofing and greater breathability...The essential combination for tent performance