The polyester high-performance fleece Cora®Deep has a fibre matrix of fine and very fine fibres. Compared to conventional fleeces, it also has a larger layer thickness. Due to the very large amount of "free pores" Cora®Deep achieved above-average dirt-holding capacity (depth filtration). The controlled thermal stabilisation of the high-performance nonwoven allows a classified separation of the particles (large, medium, fine). The Cora®Deep nonwovens are subjected to a novel surface treatment process in order to meet the increasing requirements for a minimum fibre release of filter fabrics: Glazing - a combination of flames and calendering. This means that even the finest particles (5μ, 2μ) are retained.