Bad Munki posted:

Are you sure you're not thinking of particle board? Or the people who are saying MDF is fine are thinking of particle board? Particle board is pretty standard fare in the mass-produced furniture market. It's lots of little particles of wood, all glued together. MDF, on the other hand, is super-fine wood dust with resin as a bonding agent. I know a guy who owns an aquarium store, and all the stands are made of particle board (except the ones that are solid wood.) Not a single one was made of MDF.

Particle board, while it may swell and disfigure, won't be completely compromised when it gets a little wet here and there, unlike MDF.

To be clear, particle board:


and mdf:


If you've seen MDF aquarium stands in person, well, good luck to them (and you) but if you're reading accounts on a forum somewhere from people who have built a particular design and they're saying, "I built it out of MDF," I would seriously question whether or not they know what they're talking about (they may not know the difference between particle board and MDF, lots of people don't.)

If you can keep it bone dry and seal it up all to hell, maybe it'll last, but in my experience, the increased humidity in the immediate vicinity of your average fish tank is enough to potentially compromise the integrity of MDF. It may take a while, and it may not be consistent enough to actually mush it, but it could easily sag and deform and when you go to move the fish tank some day, you may find that the stand is falling apart in places. Or it might collapse before then.