Engine blow-by is something that affect just about every engine on the road, especially on force induction vehicle that has high cylinder pressure through turbocharging, the FK8 Civic Type-R is one of the victim that made that list.
Air and Fuel combustion is what drives pistons and crankshaft. During this process, the pressure on the top side of the piston pushes combustion gasses, as well as droplets of oil and fuel, they then past the piston rings and into the crankcase, and this is what's called Blow by.
To prevent the crankcase from becoming pressurized, and causing issues with oil sealing and robbing the engine of power, blow-by is pulled from the crankcase via the positive crankcase ventilation (PCV) system and routed back into the intake. You can guess this can be problematic, as oil and fuel are not what you want in your air intake system.
One of the option is to install an oil catch can, such as the Radium Civic Type-R Catch Can PCV Type, this catch can runs inline with the PCV valve and retains its factory function. When the intake manifold pressure is close to or greater than atmospheric pressure, the PCV "check" valve closes and, thus, this hose experiences no flow. Conversely, the PCV hose will experience "metered" vacuum when the engine is idling, steady state cruising, and decelerating. This would normally draw unwanted crankcase vapor, unspent fuel, and oil sludge into the intake manifold immediately after a high load run.
Note: No inline check valve is required since Radium catch cans are pressure sealed. This means a direct intake manifold connection is permitted.