Originally Posted by Roger
The Holland & Sherry Viceroy flannels are all worsted flannels, as far as I know
Definitely not. The first several swatches in that book are woolens: various solids, stripes, windowpanes and plaids. I can't recall off the top of my head how many woolens there are, but quite a few. The designs are more classic and traditional than the designs in the Victory book.
What are the differences between woolen flannels and worsted flannels with respect to appearance (woolen flannel nappier than worsted?), wear, ability to hold a crease, warmth, etc.?
The basic difference is the type of yarn used. Woolen flannels are made with woolen yarns, worsteds with worsted yarns. The difference in the yarns boils down to the process used (or skipped) in preparing the yarns for spinning. Essentiallly, to make worsted yarns, the fibers are carded and combed out straight and flat prior to spinning. The resulting yarn is more taut and smooth and fine, and stronger. With flannels, combing (and sometimes carding) are skipped. The resulting yarns are thicker, spongier, fuzzier, and somewhat weaker and softer.
Woolen flannel will be typically thicker at the same weight, softer, spongier, and fuzzier. It will have a more "mottled" appearance. It won't hold a crease as well or perform as well, except maybe at the very heaviest weights. The 16 ounce cloths in the Minnis book are iron, for instance. Worsted flannel performs a little better, and looks a little more crisp. But it looks less like "flannel." You can typically see the underlying weave pattern more clearly. With a woolen, it almost takes a microscope. Even up close the cloth just looks like a wooly mass.
Over time, woolen flannel will bag and stretch at various stress points, for instance, the knees. It will get threadbare in the knees and seat (this is why tailors recommend two pairs of trousers with flannel suits). It will never hold a crease as well as a worsted.