The Dutch Touch PRO filter is filled with premium quality, ultra absorbent activated carbon granules. Due to its extremely porous nature, just a gram of this form of carbon has an enormous surface area of approximately 2000m² (2392yd2) ! The zinc galvanised steel walls of the Dutch Touch PRO have a perforation of R1.8.T2.5, which means each hole is 1.8mm in diameter with their centres being 2.5mm apart. This ensures that nearly 60% of filter walls are open to enable air to more easily pass through. As long as the Dutch Touch PRO filter is fitted correctly, in an environment with a maximum relative humidity of 70% or less and is operated within the specified parameters (with regards to cubic meters per hour airflow) we guarantee a service life of 18 months.