After passing through the MIZ, waves encounter thicker and older ice in the form of pack ice or fast ice. Fast ice is ice that is bound fast to a continent. Pack ice is an ice floe that is packed together by the motion of waves and winds and as the word floe suggests, pack ice is mobile. 

Sea ice acts as a low pass filter for surface ocean waves, that is the shortest waves are damped or stopped by the effect of the ice floating on the water. Short waves are also attenuated or stretched out by the influence of the sea ice floating on the water. The end result of the damping and attenuation is that only the longer waves penetrate to the interior areas of ice floes⁴.

A dramatic account of long waves propagating into the interior of an ice field is contained in Endurance which is the story of a maritime vessel's crew stranded in the Antarctice pack ice. When the crew of the Endurance is nearing the edge of the Antarctic ice floe, they become ever more aware of the long ocean swell that becomes stronger and more persistent as they near the edge of the pack ice.