this image doesnt show it particularly well, but after about 3 months of use this IMS 35µM screen is spectacularly clean

it has been stopping almost all coffee particules getting above the shower screen, which in turn means a cleaner piston - i.e. less to clean when you perform a change of piston seals

the big lumps floating around in there have dropped in there after i took the group top off and then got called away to another task for a few hours - the machine was by an open window and little bits of muck dropped into the group (much larger than the size of the mesh on the IMS 35µM)

the other reason for using an IMS 35 screen is it reduces the surge of water into the portafilter when the piston is raised - the fine mesh breaks up the surge like a breakwater and reduces the chance of washing out the top of the puck as a result