How Much Will Plywood Move With Humidity
Roughly a tenth of solid wood's movement, in-plane
- Cross-laminated veneer construction (alternating grain direction between plies)
Methodno single shrinkage coefficient applies — each ply's tangential movement is restrained by the ply above and below it running the opposite direction, which is the entire structural point of plywood.
This is a qualitative comparison, not a computed figure — plywood's real in-plane movement is small enough that most shop work treats it as negligible, unlike solid lumber.
Plywood moves roughly a tenth of what solid wood of a comparable species moves in-plane with humidity — enough that most shop work treats plywood's own seasonal movement as negligible, which is exactly why plywood gets specified for parts where dimensional stability matters more than anything else.
Why this one specifically
Every other page in this family answers "how much" with a specific number, because solid wood's movement is a single, real, measurable coefficient. Plywood doesn't have one coefficient to give — its cross-laminated construction alternates grain direction between plies, so each ply's natural tangential movement gets restrained by the plies bonded above and below it running the opposite direction. That restraint is the entire structural point of manufacturing plywood in the first place, not a side effect, which is why cabinet backs, drawer bottoms and case sides so often specify plywood over solid wood specifically to sidestep the movement problem solid panels create.
What moves the number
Panel thickness and ply count both affect how completely the cross-lamination restrains movement — a thin, few-ply sheet restrains less effectively than a thick, many-ply one. Humidity does still affect plywood's THICKNESS more than its in-plane width or length, which is a different effect from anything the solid-wood pages in this family describe.