There are a handful of trains of thought that people encounter when thinking of better ways to build Hybrids. The first one is foam, the second one is aluminum. Others include needing to use thicker wood or heavier cloth because the builder is bigger than average - it just isn't necessary. Heavier wood is heavy and heavier cloth needs more resin and is heavier then two layers of lighter cloth, which is also stronger!
I have not built a Hybrid out of foam but almost...
The blue & pink foam you see at Home Depot, Lowes, Maynards and everywhere else is not structural and actually off-gasses. What this means is that it is weak and will delaminate the eopxy resin/glass you have on it. The puncture resistance is not there and it may actually weigh more than the thin plywood & glass.
How can that be? The foam weighs a bit less than plywood, even 1/4 inch! Most of the boat weight comes in when you start putting resin and cloth on there. You'll need extra resin and cloth to do it right, at least double, possibly triple. I have done the research and spoken to some seasoned old boat builders who were nice enough to share their knowledge - the foam will weigh more! Basically after the third old boat builder told me this, I gave it up.
The aluminum factor is sweet. High tech welding, bending metal, sexy!
Problem is the metal needs to be stiffer and if you add reinforcements or thicker gauge, it weighs more! I build a 75-90 pound 10 ft Hybrid depending on what goes into it - the lightest aluminum rig will be about 115 pounds. But they last forever! The jury is out on how long Hybrids last when taken care of - an epoxy boat should last in the range of 50 years. I'll be dead before my boat rots. It is comforting.
Please don't take this wrong, I'm just sharing.
If you want to do the foam, please use something like nida-core or core-cell. I have 1/2 a honeycomb Hybrid sitting in my garage because I screwed up on an $800 material purchase. Trying to figure out how to stiffen the 1/4 inch honeycomb. I used 12 oz bi-axial (18 oz strength) when I should have just used a couple layers of 6 oz cloth.
Oh yeah - I don't know where you are but make sure the honeycomb or foam will not freeze and shatter if you hit a rock or something. I heard that some of the building materials will get brittle in the cold - kinda like PVC does. I forget what I used was called, just wish I spent the $200+ on a sheet of 1/2-inch as it would have been stiffer and there wouldn't be a half-built boat sitting in my garage...taunting me