1/4 might be too thin, if you consider drilling the hole and then trimming flush with the table saw, the 3/8" matl was pretty thin towards the opening of the hole. 3/8" will give much more thickness, and just a bit more gluing area. 3/8 is a touchmore expensive, and you do have a sheet of 1/4 to use up. I bet the 1/4 would be better used for the base, the skimmate cup, etc, but the thickness works with us in the funnels at 3/8. Just me own .02