Here are some of the forms you can buy your fibres in for felting or spinning.
Unwashed Fleece – This is greasy fleece cuttings.
Washed and Scourced Fleece – This is the washed fleece version.
Carded Batt – A carded batt is washed and scourced fleece that has been carded into a length, ready for brushing. The fibres are multi-directional, so it looks like a length of fluff!
Rovings or Tops – This is a brushed carded ‘sliver’. All of the fibres are smoothe and going in one direction.
Nepps, Knops, Burrs or Slubs – These are usually by-products of the scouring, or carding processes. They are small bobble-like bits of fleece, which are great for effects in your feltwork.
All are sold by gram, or ounce if you are overseas.
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This is also part of the Working with Felt forum.