Medium density fiberboard or MDF is best known for the flat pack merchandise.  Flat packs are the items you buy at big box stores bring it home throw some fancy fasteners on it and poof you have a bookcase, TV stand, or what have you.  The question always comes up is MDF bad for furniture.  The answer with one exception in my opinion is yes.  The one and only great thing about MDF is that unless a lot of liquid comes in contact with it in the raw form it will stay dead flat like granite counter tops.  It is not good for strength such as the sides of a book case.  We all have seen those shelves in the book case that are sagging because of the weight of the books on them.  The same applies to particle board core materials. 

          For strength the use of plywood is one of the best choices, but like every other rule there is an exception with that as well.  More on that rule later.  Case sides are a great place to use plywood.  It is a very strong and stable material.  Plus the fact that it comes in large sheets reduces the time of gluing smaller boards to attain the width desired.  However the exception to the rule and that is hardwood is nature’s best material for strength.  But to make kitchen cabinets out of hardwood would be so cost-prohibitive in reality.  So we use "sheet goods" or plywood in these instances to reduce the cost.  Not to mention make the manufacturing process easier.

          So to recap on all of this.  MDF is fine for furniture construction as long as it is used properly.  And properly I mean for surfaces that need to be flat.  This would be for table tops or shelving tops not the whole shelf just the top of it.  Plywood materials are the best strength materials that are made that wide.  It is very rare to see a piece of walnut 4 foot wide by 8 foot long.  So make sure that what ever you may have built for you or build yourself that you use the right materials for the right parts of the construction.  Any questions or comments email me directly I would be delighted to hear from you.