OK, so the project is the replacement of some wood passenger car windows, double hung sash, normal heavyweight style.

Vendor proposed a material I've never heard before - "Accoya wood" which is some kind of stabilized and 'modified' pine, with some remarkable claims for longevity, but can still be painted or stained.

Anybody hear of this or actually use this stuff for wood car components or restoration?

https://www.accoya.com/what-is-accoya/

The wikipedia entry is interesting: https://en.wikipedia.org/wiki/Acetylated_wood

Railroad car window sash etc was traditionally made from Honduran mahogany, which is unobtainium these days due to forest destruction. The same wood is now plantation-grown on the island of Fiji. I've seen 1x6 boards of this stuff at my local lumberyard (indoor storage), and it looks great: tight straight grain, clear lengths. Here is one source in the USA: https://www.mahoganyoutlet.com/plantation/

- Doug Debs

Accoya Wood was recommended to me a while back. Haven't tried it, though. It is a premium product likely with a corresponding price tag. And it's not something you can get at your local big box or lumber yard. It would be interesting to hear how it's held up over time if anyone here has tried it.