A bone cement comprising: a first powder component which contains pre-polymerised beads having a first average molecular weight and including a high molecular weight population of beads having a second average molecular weight that is higher than the first average molecular weight, and a second liquid component which contains a monomer, characterised in that the first average molecular weight, the second average molecular weight, and the percentage of beads having the second average molecular weight, are selected so that contacting the first powder component and the second liquid component produces a mixture having a viscosity profile which includes an initial period, a working period, and a hardening period, in which: (a) during the initial period, the viscosity increases over time until the mixture attains a viscosity greater than 200 Pascal.seconds within 1 minute from mixing the first and second components, (b) during the working period of at least 5 minutes, the viscosity of the mixture remains between 200 and 2000 Pascal.seconds and changes by less than 10% in a period of 2 minutes within said working time, the viscosity being measured using a capillary extrusion rheometer for measuring an applied force acting on a piston to displace the mixture in a capillary tube at a constant displacement rate, the measurements being performed at an average temperature of 22.3°C and a constant displacement rate of 3 mm.min -1, and in which the mixture is suitable for in vivo use. a first powder component which contains pre-polymerised beads having a first average molecular weight and including a high molecular weight population of beads having a second average molecular weight that is higher than the first average molecular weight, and a second liquid component which contains a monomer, characterised in that the first average molecular weight, the second average molecular weight, and the percentage of beads having the second average molecular weight, are selected so that contacting the first powder component and the second liquid component produces a mixture having a viscosity profile which includes an initial period, a working period, and a hardening period, in which: (a) during the initial period, the viscosity increases over time until the mixture attains a viscosity greater than 200 Pascal.seconds within 1 minute from mixing the first and second components, (b) during the working period of at least 5 minutes, the viscosity of the mixture remains between 200 and 2000 Pascal.seconds and changes by less than 10% in a period of 2 minutes within said working time, (a) during the initial period, the viscosity increases over time until the mixture attains a viscosity greater than 200 Pascal.seconds within 1 minute from mixing the first and second components, (b) during the working period of at least 5 minutes, the viscosity of the mixture remains between 200 and 2000 Pascal.seconds and changes by less than 10% in a period of 2 minutes within said working time, the viscosity being measured using a capillary extrusion rheometer for measuring an applied force acting on a piston to displace the mixture in a capillary tube at a constant displacement rate, the measurements being performed at an average temperature of 22.3°C and a constant displacement rate of 3 mm.min -1, and in which the mixture is suitable for in vivo use.