Rubber bits from Sprenger are made of soft but tough rubber that has a Stainless steel cable inside to reinforce the mouthpiece. Rubber generally has an 'eraser-effect'. It is therefore important that horses are salivating and chewing well when using these bits. If the horse does not produce enough salvation the rubber bit will be uncomfortable. Different from pure metal bits there is the danger of the rubber being easily bitten through when the bit is nto attached correctly and gets into contact with the teeth.