Ted commented: "I think, oh Alpaca Guru, that it would be great if you did an anatomy lesson of an alpaca fleece. I keep hearing about this 'blanket' thingy, but have no idea why it's important."
I don't know that I really qualify for guru status, but I did a quick Google search (for alpaca fleece diagram, I think) and found this. In this particular diagram, the blanket is labeled as "saddle", which is an alternate term. The blanket area of the fleece is generally the area with the finest fiber and the fewest guard hairs. In high quality animals, the neck fleece is often comparable, and these prime areas when clipped are generally referred to as "firsts". The "firsts" are usually clipped first & bagged separately.
The "seconds" - usually the middle leg, apron, +/- neck - are then usually clipped and bagged separately. The "thirds" - lower leg, britch (usually), tail, belly, topknot - are generally either bagged separately or discarded, depending on quality. Some farms will only shear the blanket & belly (maybe the neck) for coolness in the summer, which is referred to as a "barrel clip". Aesthetically, I think this looks silly. It also leaves some potentially usable - not to mention potentially very warm - fleece on the animal during the summer months.
The reason guard hair content is important is that it affects the comfort level of the finished textile. As a rule of thumb, fibers of greater than 30 microns in diameter will make the wearer feel prickles when wearing the garment next to their skin, so the goal is to have as few of these coarse fibers as possible. This is why merino, which has a low average fiber diameter, can be worn next to the skin, while many other wools cannot.
Because in alpacas these larger diameter fibers are usually guard hairs, the fewer the better. Below 30 microns, hand feel is affected both by average fiber diameter and by scale structure on the individual fibers (All mammal hairs have scales, to greater or lesser degree, along the hair shaft - perhaps a little reminder of our reptilian origins?). An animal can have an average fiber diameter that is relatively higher, but if there are very few guard hairs and very few or very small scales on the individual fibers, then it will feel slicker and smoother to the touch than fiber that has a lower average diameter but either a greater percentage of guard hairs or more prominent or numerous scales on the individual fibers.
How's that for a primer?