Don't call it a compromise.

What plywood actually is

Plywood is thin sheets of wood (veneers) glued together with the grain of each layer rotated 90 degrees from the one next to it. That cross-grain construction is what makes plywood almost indestructibly stable. Solid wood moves with humidity because wood expands and contracts along one axis more than the others. Cross-banded plywood has its axes fighting each other in every layer, so nothing ever wins. The sheet stays flat.

Birch vs spruce — the one decision that matters

WISA makes plywood from two species. They are not interchangeable and they are priced differently for good reasons.

Birch is a hardwood. The face is smooth, hard, and light-coloured. It takes stain and clear finish beautifully. It's stronger per millimetre, so thinner panels work for the same load. It costs more. Use it where the panel will be seen or where you need maximum strength in minimum thickness.

Spruce is a softwood. The face has more visible growth, character, and occasional knots. It's about half the weight of hardwood alternatives. It paints well. It costs less. Use it for walls, roofs, floors, shop projects, and anything that'll be hidden or painted.

Grades — what they actually mean

The grade of a plywood panel (BB, WG, III, and so on) describes what the face looks like, not how strong the panel is. A lower grade panel has the same glue, the same cross-banded structure, and the same load-bearing capacity as a higher grade panel. The only difference is visible knots, patches, and surface defects.

This means you should almost never pay for a higher grade than you need. If the sheet will be painted, hidden behind cladding, or used as a template that gets thrown away, buy the cheapest grade. Save the premium-faced stuff for work that will be seen.

Thickness and sizing

WISA panels come in thicknesses from 4 mm up to 50 mm for structural spruce, and standard sheet sizes around 1220x2440 mm, 1250x2500 mm, and 1500x3000 mm. Larger sizes are available on request, which is one of the quiet advantages of buying from a real plywood mill rather than a hardware store.

One thing every beginner learns the hard way: the nominal sheet size is slightly oversized. A "2440x1220" sheet is usually somewhere around 2450x1225, with rough edges. Trim all four edges to a known reference before you measure for anything else. See the blog post below for more on that.