Flower stems are often bound together with an elastic band or other type of binding material. Although it is common practice, some binding materials can have a negative effect on the vase life. Elastic bands are no problem; they are made of an inert material. Natural fibres, such as raffia, rope etc., cause problems if they are biologically contaminated. In addition, they can serve as food for bacteria that may be present, particularly in vases only containing tap water i.e. no flower food.