I'm glad you are happy with your new alpaca sweater.
Alpaca fibre comes in a range of qualities, just as sheep wool does. The higher the quality, the more you pay. There are relatively few alpacas compared with sheep so it is rarer and costs more. As with all animal fibres, though, the processors put a premium on the product so what the final product costs bears very little resemblance to what the farmer actually gets for the raw product. Because alpaca is a bit more unusual it has more 'scarcity' value or 'exotic' value. It also has qualities that sheep wool doesn't have, and can produce lovely soft, light fabrics and woollens.
Alpacas and llamas are both used for fleece production but generally alpacas have finer fleece than llamas.
Alpacas (and llamas) have a fleece made up of 2 types of fibre, like most other fleece bearing animals, including sheep. From each hair follicle in the skin they produce at least 1 'guard hair', which is straighter, stiffer and takes dye less well, and several fleece fibres, which are the soft, silky, smooth ones. The more of these second type of fibres in a section of fleece, the better. The more of the guard hairs, or primary fibres, the more prickly and itchy it will feel.
Fleece producers aim to breed fleeces which have lots of the nice soft fibres and very few of the prickly guard hairs. In processing, the guard hairs can be taken out, which is what happens with cashmere, but if the processor doesn't bother with this and if the fleece is of poorer quality (i.e., it has a lot of guard hairs in it) then the final product will tend to be more itchy and prickly. This is sometimes referred to as the 'prickle factor'.
You will find exactly the same thing with sheep wool. In good quality sheep wool, there are relatively few prickly guard hairs, or they have been bred to be finer and softer (more like the nice fleece fibres), or they have been removed in processing.
The better the fleece, the more it is worth. Also, the better the processing, the more the customer pays.
