Buying handspun is a magical thing - whether you work with it, give it to someone as a gift or just put it in a glass bowl and look at it! But if you're planning on working with handspun, you'll need to know a few things to help you make the perfect choice for your project.
The key elements you need to consider are content and weight. I've set out some of the main options here.
For handspun yarn, many people use "WPI" (wraps per inch) to determine the yarn's weight (or thickness). The yarn is wrapped around a tool and then the number of wraps in an inch is counted. For extra accuracy, wraps in 2 or 3 inches can be counted and averaged out.
More than 18wpi is a laceweight yarn, also known as 2-ply. It calls for 2.25-2.75mm (USA 1-2) needles.
16wpi is a fingering weight yarn, also known as 3-ply. It calls for 2.75-3.25mm (USA 3) needles.
12wpi is a sport weight yarn, also known as 4-ply. It calls for 3.25-3.75mm (USA 3-5)needles.
10wpi is a double-knitting or DK weight yarn, also known as worsted. It calls for 3.75-4.5mm (USA 5-7) needles.
8wpi is an aran weight yarn, also known as fisherman or medium. It calls for 4.5-6mm (USA 7-10) needles.
6wpi and under is a bulky yarn, also known as chunky. It calls for needles in sizes upwards of 6mm (USA 10).
There is some flexibility in these figures, but these are what I have found to generally be correct. Don't be scared to experiment - you can get great results. For example, knit up a lace pattern in sock weight yarn on 5mm needles or create a densely knitted and warm hat by knitting with aran weight wool on 4mm needes.
These days yarn can be made from absolutely anything. From traditional fibres like wool and cotton to recycled jeans or a huge range of acrylics. I'll list here any fibre I have used so far, and add to this when I use a new fibre.
Wool This is the obvious one - but it's not as simple as you think. There's a huge variety of breeds, and the fleece of each breed has different properties. For example, Merino sheep produce amazingly soft and fluffy wool, whereas Corriedale wool is not as soft but is more hardy. Wool can felt, so woolen garments should be washed gently (usually by hand) and dried flat - unless felting is what you want. Wool can be treated to make it more washing-friendly . Wool that has been treated is called 'superwash' and will not felt.
Silk Silk is a natural fibre, which has been the ultimate in luxury for centuries. It is made by silk worms as their cocoon, in which they develop into moths. It comes originally from the far east, but can now be cultivated nearly anywhere in the world with the right equipment.
Tencel Tencel is a man-made fibre, but in contrast to traditional mandmade fibres such as acrylic (which are made from fossil fuels), Tencel is processed from trees.
Alpaca Alpacas are amazing animals which come originally from South America but are now farmed all over the world. Their fleece is supremely soft and fine. It is ideal for use in clothing because it is temperature regulating - cool in summer, warm in winter. I didn't beleive this myself at first, but I store all my yarn together in plastic crates and on warm days, the apaca feels cooler than the wool.