Process for coating the surface of a plastic substrate, with the following steps: A. providing the plastic substrate and optionally cleaning the surface of the plastic substrate to be coated, B. coating the substrate surface, optionally cleaned in step A, by plasma polymerisation in a high frequency plasma polymerisation reactor, wherein in step B - as precursor(s) for the plasma one or more siliceous organic as well as (a) no further or (b) further compounds are applied and the plastic substrate is arranged in the high frequency plasma polymerisation reactor such that it is located between the zone, in which the plasma is formed, and the cathode, an adjustment setting takes place, such that the self-bias is in the range of from 100 to 300 V, characterised in that the process is performed such that the coating manufactured by the process has - a fraction of carbon of from 3 to 28 atom-%, preferably 5 to 28 atom-%, more preferably 7 to 28 atom-%, referred to the total number of the carbon, silicium, and oxygen atoms contained in the coating, which can be determined by XPS measurement - a fracture distension of ≥ 2.5 % - a Yellow Index determined according to ASTM D 1925 of ≤ 3, preferably ≤ 2.5 and - a hardness to be measured by nano-indentation in the range of from 2.5 to 6 GPa, preferably 3.1 to 6 GPa. A. providing the plastic substrate and optionally cleaning the surface of the plastic substrate to be coated, B. coating the substrate surface, optionally cleaned in step A, by plasma polymerisation in a high frequency plasma polymerisation reactor, wherein in step B - as precursor(s) for the plasma one or more siliceous organic as well as (a) no further or (b) further compounds are applied and the plastic substrate is arranged in the high frequency plasma polymerisation reactor such that it is located between the zone, in which the plasma is formed, and the cathode, an adjustment setting takes place, such that the self-bias is in the range of from 100 to 300 V, characterised in that the process is performed such that the coating manufactured by the process has - a fraction of carbon of from 3 to 28 atom-%, preferably 5 to 28 atom-%, more preferably 7 to 28 atom-%, referred to the total number of the carbon, silicium, and oxygen atoms contained in the coating, which can be determined by XPS measurement - a fracture distension of ≥ 2.5 % - a Yellow Index determined according to ASTM D 1925 of ≤ 3, preferably ≤ 2.5 and - a hardness to be measured by nano-indentation in the range of from 2.5 to 6 GPa, preferably 3.1 to 6 GPa. - as precursor(s) for the plasma one or more siliceous organic as well as (a) no further or (b) further compounds are applied and the plastic substrate is arranged in the high frequency plasma polymerisation reactor such that it is located between the zone, in which the plasma is formed, and the cathode, an adjustment setting takes place, such that the self-bias is in the range of from 100 to 300 V, characterised in that the process is performed such that the coating manufactured by the process has - a fraction of carbon of from 3 to 28 atom-%, preferably 5 to 28 atom-%, more preferably 7 to 28 atom-%, referred to the total number of the carbon, silicium, and oxygen atoms contained in the coating, which can be determined by XPS measurement - a fracture distension of ≥ 2.5 % - a Yellow Index determined according to ASTM D 1925 of ≤ 3, preferably ≤ 2.5 and - a hardness to be measured by nano-indentation in the range of from 2.5 to 6 GPa, preferably 3.1 to 6 GPa.