The apparent thermal expansion of cellulose immersed in liquid water, d⌀₂/dT, is several times that of dry cellulose. A similar but greater disparity is observed when the temperature dependence of the apparent specific volume of glucose in aqueous solution is compared with the thermal expansion of crystalline glucose. This effect appears to be a general one for polyols such as glucose and glycerol and can be interpreted in terms of a ‘mixture’ theory of water structure. Water is pictured as being made up of small short-lived clusters which may be classified as either solidlike or fluidlike. The solidlike component consists of rigid, hydrogen bonded ring structures (tetramer, pentamer, hexamer). The fluidlike component consists of non-rigid, less hydrogen bonded, chain structures (dimer, trimer, star pentamer). Surfaces rich in hydroxyl groups appear to act as structure breakers by causing an increase in the proportion of the fluidlike component in the water adjacent to the interface. With cellulose, this perturbed layer consists of the non-rigid chain structures, hydrogen bonded to the -OH groups on the surface. The high values for d⌀₂/dT for glucose and cellulose are caused by the high thermal expansion of the perturbed layer.