For my question I'm relating to traditional straight or slight backset longbows. But please specify what type of bow and what your thoughts are on glass to wood ratio.
I guess I never thought about the glass to wood ratio.
One of my recent straight longbows had a total stack thickness of 0.440" and I used 0.050" glass on the back and belly, so thats 0.100" glass to 0.340" wood and a ratio of 0.294. It was 68", 63# @ 28", and 1.25" wide at the fadeouts tapering from mid limb down to 0.5".
Now I'm not sure how it would have turned out if I would have used 0.040 glass (0.080 total glass) and 0.360 wood. Probably close to the same weight, but I'm not sure. Maybe one of the professional bowyers will be along to offer advice.
From what I have been told on here in the past, the thickness of the glass doesn't really matter, its the total stack thickness is what is important. Just don't use .030 glass on heavy draw bows.
For a longbow the glass to wood ratio should be between 20 - 25%. and for a recurve the ratio should be between 30 - 40%. Your bow will still shoot if you're outside of these boundaries but the limbs might get a bit flabby if the ratio is to high.
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Andy