There is no such thing as HDF.
Did I get your attention? I’ve said something like that before in blogs, but I think it’s time we make a blog just on this topic. With the new EPA reg about formaldehyde moving into place, there should be a renewed focus again on what types of products get regulated by what aspect of this rule (or CARB).
So what is HDF? In short, it’s really a marketing term. My belief is that it was popularized in large part by the laminate flooring industry. We all remember early laminate, which just didn’t perform properly in use. The industry adapted by using a higher density core and made sure to distinguish it from the earlier production by calling it HIGH Density Fiberboard—this was to reassure customers that this was somehow a new better product. But technically and legally, it’s still MDF.
So what is MDF? How did we come up with that term? The way I understand it is that when MDF was first developed, it looked a lot like an existing product called “hardboard” and of course it is made of fibers. So logically it came to be called “fiberboard.” There was already a “low density” product out there, and this new fiberboard had a “middle of the road” density level in comparison, so it was therefore called Medium Density Fiberboard. (In the early days, the typical MDF density was around 48 pcf (per cubic foot), ranging a bit lower for thicker products and a bit higher for thinner material.)
Over time, continuous MDF presses became more popular. This type of equipment is particularly proficient at making the thinner panels that are used in laminate flooring. These presses could easily and economically produce material in the 55-60 pcf range. Some producers called it “high density MDF.” Since HDMDF sounds strange, that got shortened to HDF. And as noted earlier, making a distinction between MDF and HDF was one the laminate industry found useful for marketing.
“MDF,” as defined by the ANSI standard (A208.2-2016 (newly updated!)), covers material in the density range of 31-62 pcf. In ANSI, this range is listed as “typical,” so some products that are higher or lower can still be called MDF, but for the most part any panels higher than 62 pcf are usually (but not always) considered hardboard. That’s important because CARB and the EPA regs both cover MDF, but not hardboard.
(And for you super nerds out there, hardboard is subject to its own various ANSI standards depending on application. It would be "Basic Hardboard” (ANSI A135.4-2012), “Prefinished Hardboard Paneling” (ANSI A135.5-2012), and “Engineered Wood Siding” (ANSI A135.6-2012)), thus helping to further discriminate. Again, hardboard is not covered by either CARB or the new EPA rule.)
Here’s a really important fact. The grades of MDF are based on physical properties, not density. It is the performance factors, not the density, that is important.
“Grade 170” is generally the grade specified for laminate flooring (as stated in the ANSI property table) and it has the highest minimum MOR/MOE/IB specifications of all the MDF grades. (Wasn’t that a mouthful? Maybe if you’re lucky, we’ll cover Modulus of Rupture (Bending Strength)/Modulus of Elasticity (Bending Stiffness)/Internal Bond (Glue Bond Strength) in a later blog…)
Now in the unlikely event a 28 pcf panel could meet the specified properties, it could be sold as MDF Grade 170. However manufacturers found early on that in order to meet the higher performance requirements of laminate flooring they needed to produce at the higher end of the density range typical for MDF—the higher density followed all the other physical requirements, not the other way around. The 170 grade standardizes the minimum physical properties, but not the density.
Why is this important? Well again, among other things, the CARB and EPA regs do not reference HDF, only MDF. The only difference noted by CARB/EPA in MDF is thin (<8 mm) or thick (everything else). There is no reference to density. If you say you are using CARB-certified HDF, technically you are misspeaking, and with all the lawyers watching the industry these days, do you really want to misspeak about something so significant?
And for those of you out there who aren’t convinced yet that we should really talk only about MDF, how about this? It so happens that in German the HDF acronym has entered common usage in texting and elsewhere … it stands for “Halt Die Fresse” or, in English, “Shut up.” Since MDF doesn’t appear to have a similar unfortunate association, maybe this is another reason we should we “halt” our use of “HDF?!”