Boron fibres

Boron fibres predate carbon fibres as high-modulus reinforcement materials. However, boron has largely been replaced by carbon because of the high cost of the former.

They do not differ greatly from glass fibre in tensile strength, but have up to five times the modulus. As the purpose of reinforcement is generally to stiffen, this is a great advantage. Because of the high price, their use is generally confined to niche markets, where its modulus advantage over carbon fibre is essential.