After my last post another friend wrote to ask about the archival qualities of hardboard for painting and specifically about a particular company that makes prepared boards artists. I don't believe in speaking badly of anyone's business. So, I'll just give my advice and let you decide.
The bottom line is... it's wood pulp (think sawdust), pressed together. it's the same material as cardboard, or the other inferior papers from the previous post.
Yes, It's pressed to lay flat and not warp but it's primary intention is for the inexpensive, disposable furniture of today. Disposable and inexpensive are the things that concern me.
It's held together with glue (sometimes) but I can't help asking myself, what happens when the glue looses it's strength and becomes brittle as all glue does?
If you use any board to paint on, it's a good idea to coat both sides and especially the edges or moisture will get in and destroy your board.
The above said, sealed properly, hardboard is an absolute pleasure to work on and is actually much more stable than a stretched canvas of any variety.
I've painted on hardboard, primed it myself and left the panel outside for a year in all sorts of weather as a test, with no damage.
Still, if you're asking I assume you want to use the best. If you want to paint on panel, I'd suggest using real wooden panels. I've seen pieces in museums that were done hundreds of years ago that look like they were done yesterday without a single crack or any sign of damage.
Final Note of Interest
In the past several years there's been a lot of talk about aluminum dibond. I don't know much about it yet but that might be the logical next step. Paintings have been done on cooper for hundreds of years and again, they've held up beautifully.