Plate foam

Plate foam is a thin layer of foam, often only a millimeter or two thick, positioned directly beneath the plate that holds the switches, sitting between the plate and the PCB. Because it sits closer to the switches than case foam, it targets a slightly different part of the sound profile.

Where case foam mainly fills the larger empty cavity below the PCB to reduce hollow resonance, plate foam dampens vibration transferred through the plate itself, which can reduce higher-pitched ping specifically. Many enthusiast builds use both plate foam and case foam together for a fuller effect, though some combinations muffle the sound more than a builder wants.

When adding plate foam, check that its thickness does not interfere with switch clips or PCB components, since foam cut too thick can prevent switches from seating fully in their plate cutouts. As with other foam mods, more is not always better, and some plates sound best with a thin, precisely cut layer rather than a dense fill.