Flexible sheet materials suitable for use as thermal insulating materials, for use in greenhouses, comprise a substrate formed of at least two cross-laminated layers of monoaxially stretched polyolefin having laminated to one side thereof a layer of a thermoplastic sheet material bearing a reflective layer formed of a metal. The substrate may be clear or opaque. When clear, the thermoplastic layer may only be partially metallised, for example to give a reflectivity of from 20 to 80%. The invention further provides a sheet material comprising a clear substrate bearing a layer of a thermoplastics material having a reflective layer formed of a metal in which the thermoplastic layer is only partially metallised.
