Yes, a 3/4"x4x8 sheet of mdf weighs in right at 100lbs. Ive weighed one. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
If you really want to know what the weight is of MDF, ask to see the MSDS Sheet for the material which will state on it the PCF weight ( Pounds Cubic Foot ) and whatever that number is divide by 12 and ya got your Lbs per sq.ft.
I also recently discovered that there is " Light " MDF which falls between Standard and UL MDF.