jkilroy, we are talking about thickness here, not width, right? You are looking at Rainy's Evazote sheet foam in the Feather-Craft catalog in 1/4, 3/16 & 1/8 inch thickness, is that correct? To answer your original question again, I would go w/ 1/0 or larger for the 1/4" foam. I would use the 3/16" foam for sizes 4-1/0 and the 1/8 inch foam for anything smaller. Although if you go much below size 8 the 2mm craft store foam would serve you better as it is thinner than 1/8". As I stated before you can double up the thin foam to accomodate larger hook sizes, so generally the thinner foam is more versatile.

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Ron M