Castanets are traditionally made from wood - the harder the wood, the better the sound. The traditional wood for castanets is granadillo. Ebony, rosewood, pomegranate and oak also give a good sound quality.
The more you use wooden castanets, the better they sound. To play at their best, they must also be kept warm and dry (many flamenco dancers keep their castanets in a woollen sock!). Excessive cold, heat or hard knocks can crack or break wood castanets.
Modern castanets are often made from pressed canvas or fibreglass because those materials are more resistant to knocks and temperature variations. Many dancers still claim the sound improves with playing and that they must be kept warm, like the wooden ones - however I'm not convinced it makes any difference at all to fibreglass castanets.
Always, always buy professional castanets. Don't be sucked in by descriptions like "semi-professional" or "student" - they're tourist quality and will sound awful. A good pair of castanets will last you for life so it's worth getting it right first time.
Take care to buy the right size castanet. If they're too big, you won't be able to control them. A castanet should be smaller than the palm of your hand - but not too small, or you'll have trouble doing rolls.
Unfortunately, there's no standard sizing for castanets. You'll see recommendations that children should play size 3, or women should play size 6, or men should choose size 8 - but that's meaningless unless you know what make of castanets they're referring to.
A good guide is to measure the width of your palm, just under your fingers. If you choose a castanet that's the same width or slightly less, they will probably be about right. Don't buy a pair that is even a little wider, though - they will be too big.
Thank you for a great post
A good guide is to measure the width of your palm, just under your fingers.