Foam is made by EVA and Poron,Poron is most durable and EVA is most soft.
3 mm for standard spacebar of using in modifying of sound.
1 mm for adjusting the special spacebar because of the different height,like SA profile spacebar etc.
Poron is used under the plate,so you need cut it before using according to your keyboard of model in spacebar of place.
Note
It can only be used in MX mechanical keyboard,please choose 6.25u or 7u as your needing.
For some special keyboards like NCR-80,it will influence the using of spacebar,you can just cut a little to change the situation and fix it,please note that before order.
