Plywood everywhere water can reach, and it is worth paying for. Your boxes are most of why custom cabinets run $500 to $1,200 a foot against $100 to $400 for stock. A particleboard base that has swollen costs $400 to $1,400 to replace.
Ask Custom Cabinets Lynn what your boxes are made of and we name the panel on the order, so you can check it when it turns up. Most quotes you get leave that line vague. It is the half of a cabinet you never see, and the half that decides how long the rest lasts.
Dry and level, both will hold your shelves up fine. Particleboard is wood chips and glue pressed into a flat sheet. It is stiff, cheap, and it barely moves with the seasons. Plywood is thin layers of wood glued with the grain running in alternate directions, which makes it strong across the panel as well as along it.
Water is where they part company in your kitchen, and it is not a slow difference. Particleboard drinks through a cut edge, swells to nearly double thickness, and never comes back down when it dries. The usual version is your sink base. A fitting weeps for a year, nobody notices, and the floor of your cabinet goes soft in the back corner where the trap drips. Plywood in the same spot goes dark and stays flat.
So we spend your money where the water is. Your sink base, the panel beside your dishwasher and your toe kicks get 3/4-inch plywood. If you want to know what is in the glue, ask for PureBond panels from Columbia Forest Products, which are made with no added formaldehyde.
There is one question worth putting to any box before you buy it. How much weight is one of your shelves rated to carry? Our cabinet cost guide prices the difference, and refacing over particleboard boxes covers the ones you already have.
Related questions
Is plywood worth it through the whole kitchen?
In an older house, usually yes. Your wall cabinets hang off screws driven into plaster and lath rather than into anything reliable. If the budget only stretches so far, put it into your sink base, the panel beside your dishwasher, and any run against an outside wall.
What about MDF?
It sits between the two and takes paint better than either, which is why you see it in doors more often than in boxes. Around water it behaves like particleboard, so we keep it out of your sink base for the same reason.
Can I tell what my current boxes are without pulling anything apart?
Open a door and look at the raw edge at the back of your shelf or your cabinet floor. Plywood shows thin stripes of layered wood. Particleboard shows you a speckled surface with no layers in it at all.