This invention relates to a composition, a process for producing a composition, a timber formulation, a process for producing a timber formulation, a construction comprising the timber formulation and a use of the construction comprising the timber formulation are herein disclosed. The composition can include a Cu-salt, a first cyclic organic compound comprising a B heteroatom and at least one further B-free cyclic organic compound. The composition and timber formulation herein disclosed are designed as wood preservatives and may be used as part of a timber preserving treatment.