Though blends vary in size of the pieces, density, moisture, etc., I think the posts above cover the ground pretty well. I would add that with any blend you pack partly by feel. There has to be air flow through the bowl to create an ember, so even if you were packing your pipe blindfolded, or just not paying much attention, you could probably get it correct by feel. You never want the leaf jammed down tight, and you don't want the bowl skimpy and altogether loose, so experience will teach you to know when the pressure is correct.