Hi Flash:

Someone else posted Extira. That would work for what you want.

Do NOT use MDO. MDO is plywood with exterior glue and waterproof paper
laminated to one or both sides. It's great for signs, provided the
edges are banded with solid wood and nothing is nailed or screwed into
it. MDO gets recommended a lot, and I used to recommend it myself, but
I've seen what can happen if moisture finds it's way into a panel. It
rapidly rots away from the inside out. I don't recommend it any more.

Regards,
John.

Flash Gordon wrote:
I was watching a show recently and a comment was made about some
material that they were using. It came in 4 x 8 sheets like MDF but
was rated for outdoor use. Anyone know what this stuff is?

I was thinking about looking into possibly using it for a garden
window, which would ultimately be painted. Any comments? Alternate
suggestions?

Thanks in advance.