Archival wood for a negative box?

Am having my processor cut and sleeve my 6x7 negatives in 5 image lengths.
Now I have an odd size for storage, so need to build a box or cabinet.
Does anyone know what plywood I could use that would not give off a harmful gas.

Thanx, Alan

All wood is harmful for long term storage of photographic materials.

I guess I'll start searching for something metal.