E. F. Linssen & L. Hugh Newman, The observers’s book of common british insects and spiders, Londres, Frederick Warne, (1953), 1958, p. 60-61.

Many different materials are used by the Caddis larvae in the construction of their cases. Those living in still waters make their cases as light as possible to facilitate movement, whilst those in running water tend to make use of heavier material, such as sand or tiny stones, which will act as ballast. ../… A denuded Caddis larva will make itself a new case in little  more than an hour, incorporating any material which may happen to be at hand.