Some varieties, like CT Shade, Sumatra and Besuki, are not particularly useful as fillers, since they just don't offer enough flavor body or mass. Some varieties are particularly good at tensile strength, and so make handy binders. Shade-grown leaf (of any variety) is intended as wrapper, but may be slightly flawed, and so is demoted to binder class.
That having been said, any variety may be used as wrapper, binder or filler. Wrapper and binder are, in a practical sense, designations of how intact the leaf is, how large the leaf is, and perhaps how sturdy or thin the leaf is. As a home-grower, I can attest that any leaf from any variety that is large enough or "pretty" enough can serve well as wrapper, and ditto for the same with a few unfortunate holes, for use as binder. The priming level determines the color of the leaf and the thickness of the leaf (as well as the nicotine and flavor intensity). The hard and fast definitions of wrapper or binder or filler are commercial classes. While they do give a hint as to use in a cigar, you can safely ignore them, and use any of them as you like.
The upper leaf of some of my cigar varieties make spectacular maduro and oscuro wrappers--commercial class be damned.
I would interpret those commercial classes with the same certitude that one might categorize what foods are breakfast vs. lunch vs. supper. So mix and match. Roll whatever you like. Since the highest grade wrapper leaf is only a minority of a specific crop, and is handled with extra care at every step, those cost more.
When I receive a bag of "filler" tobacco from Wholeleaftobacco.com, I will often sift through it for any likely wrappers, and usually find at least a few half-leaves that do make good wrappers.
Bob
