National Fiber's Cel-Pak is, like most things, a much better product than you could buy in the 1970's. First, it's completely fiberized, which allows for interlocking of the cellulose fibers. Then there's the equipment and techniques used to install it - both radically improved from the 'good old days'.
Today, Cel-Pak is 'dense-packed' in walls at a density of 3.2 - 3.5 lbs of material per cubic foot of space, or more than twice its settled density. This does a couple of things. First, the installation process ensures that cavities are completely filled - no gaps, no voids, no pockets or spaces.
Second, using 3.5 lbs. of material per cubic foot ensures that the material is under slight pressure in the wall cavity. It simply can't settle, because there is no room for it to settle. (Those displays you see at trade and home shows showing cellulose blowing around in a box? They're designed to trick you, using far less material than is installed in the field, so don't be fooled.)
The bottom line
Cellulose has improved in quality and sophistication over time, and it now provides exceptional resistance to fire, moisture, mold, and vermin. What other insulation can claim these benefits and also provide the superior thermal and sound insulation that comes naturally to cellulose?