There are hundreds of different profiles of moulding and within each profiles there are three different types and those different types have a different purpose and cost depending on how they are made.
Traditional real wood is what most people associate with moulding, but that is also the most expensive. Typically, pine or oak, these are the most common real wood moulding, there are more wood species depending on your needs. The manufacture must make sure the wood is straight, has few or no knots in the grain and has just the right amount of moisture content otherwise; the strips of wood will warp.
When you want to show off the grain or stain the wood to match your décor, real wood is the way to go. Also, more companies are producing prefinished moulding to match their cabinets or other wood items to keep the finish consistent and or give the customer/contractor the ability to save some time not having to finish the moulding themselves. In addition, one more feature to point out, the length of the tree dictates the length of the moulding, so there are limitations to using real wood.
Other than real wood the kind of moulding is Primed Finger Jointed—better known as PFJ, this is several scraps of real wood with “fingers” cut into each end of the of the wood, as to interlock the pieces of wood to make longer pieces, some can be longer than 16 feet.
Once the longer pieces are created, the wood goes into a shaping machine. Once the profile is created, a primer coat of paint is applied at the factory, then the customer must apply a final coat of paint to match their décor; the paint is needed in order to hide the “fingers” where the wood is joined together, piece by piece.
The final type moulding is MDF, which stand for Medium Density Fiberboard. MDF is a collection of sawdust, wood shavings, small wood chips, and resin that provides a uniform material for cutting, nailing, and painting. It is less expensive than finger-jointed trim, so if you are trimming an entire house, the cost difference can be substantial. MDF is heavy and floppy, making it difficult for one person to handle and install. Long lengths are also more prone to breaking than finger-jointed pieces.
The material’s flexibility means that it will follow any waves in the wall rather than simply running over them. The edge strength on MDF is low, so outside miters must be handled with care to avoid chipping. Because the material has no grain to grab onto nails, withdrawal strength is low. It is best to install MDF with an adhesive, using nails as clamps while the adhesive dries, or no adhesive at all. MDF swells in wet areas or areas with high humidity, so it’s not good for bathrooms.
Cutting MDF produces a very fine dust, so it’s best to do it outside while wearing a tight-fitting dust mask or respirator, or if you plan on cutting inside, use a vacuum to collect the dust and still wear the mask. Because MDF is extruded, the manufacture is able to create very long lengths of moulding and it is very consistent in shape, which is great for when you want few or no seams to join.