News to me - doubt that's possible - it's makeup would be like a sponge outside. Although one could cover it w/waterproofing substances, it's still wood, which w/eventually break down.

Ya, that's news to me if they make it for outdoors...but now ya got me curious...I gotta go find out!ha! Canada is behind with stuff that You guys get. We don't even have a good source for that stuff/cement board with the foam inside yet.

It's known as MDF MR, 'Moisture Resist' in Australia.
Been available for a couple of decades but is not for outdoor use. We used it in top end kitchens and dental cabinetry, the company I worked for wouldn't touch the regular MDF in kitchens.
MDF as we buy it from the hardware store didn't take off in the States for a long time because of the Formeldyhide content. The Americans couldn't convice the customer that the product is safe to the end user. Unless it's sawn up and and the dust is inhaled, it's fine.
I tossed all the building safety stuff I had before I left Australia but Laminex Industries and Formica, the forestry division, another name I think, used to have some info.
I don't know if the bonding agents have changed but MR is available in Nth America, it's a bit coarser than the Aussie stuff and is tough to cut without a power saw. Don't hold me to this but I think it is a Georgia Pacific product.

NB. IMHO, it took Aussie and UK carpenters/joiners on TV to get it on the market over here! I had to special order the stuff when I built my desk in '97.

Weathertex signboard.Used outdoors for signage.

Durable.