Does anyone know anything about foam? (upholstery)

[The brew guy 22]

So I had a bright idea about re-doing the interior of the boat over the winter, at the rate I'm going it'll be done a by next winter. Two of the projects involve foam and I've been reading about foam for 2 weeks but haven't found the information I need.

One of the projects is the dinette. The upholstery isn't bad, but the foam is shot so it's like sitting on plywood. We got some material and will be replacing the fabric but I haven't figured out what foam I need. I've dissected a couple of cushions and the base is 3/4" plywood with 2" foam and a few layers of cotton looking stuff over it. As is often the case on a boat, the table drops down and a filler cushion turns the dinette into a third bed. The filler cushion is in great shape so I hadn't planned to replace it, this means I need to stick with the same height for the cushions so it all matches. Besides, I'm willing to assume the 2" foam was adequate when it was new, so it should be enough now, right?

The other foam project is the forward bunk, This is my bed and I spend 60-80 nights per year in it so I want it pretty nice. This also has 2" foam and I bottom out on it. The aft cabin has the same foam and it's in much better shape, so I know it could be done in 2 inch again. Still, I'd like to do better than that, but I know it can be done in 2" if I use the right foam. I got through last summer by adding a piece of carpet padding under the foam and putting on a memory foam topper. I really didn't like the memory foam. I'm willing to go with thicker foam if it will help. The design of the bunk includes a "flange," for lack of a better term, around the outside edge that would lend itself to having a 3/4 or 1 inch foam underneath a thicker, top layer. I'm thinking of a bottom layer of firmer foam covered by 2" of medium foam. It seems like a good idea to me, but I know nothing about this stuff.

Like I said, I've been reading about foam for a couple weeks. I've got a basic understanding of density and ILD, but no idea what numbers I need to use so my butt isn't on the plywood anymore. Full disclosure; I'm not skinny, in case it makes a difference. Is an ILD of 35 enough for a 2" seat cushion? 40? 50?? For the bed, same thing, 35? 40? 2 inches or 3? All one foam, or put something firmer under it? Any help would be appreciated, I seem to have confused myself.

[A-Tech 8]

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