The research reported here is concerned with optimizing the combined use of two different fibre types in cementitious matrices. The two fibre types were a high-modulus polyethylene fibre and a fibrillated polyethylene pulp. The effects of different volume fractions of the two fibres and their interaction on the impact resistance, flexural strength and toughness, compressive strength, bulk specific gravity, volume of permeable pores and water absorption capacity of cementitious materials manufactured with a highperformance mixer were investigated through a factorial experimental design. In the case of impact resistance, the positive effect of each fibre was pronounced in the presence of the other fibre type, For flexural strength and toughness, the combined use of polyethylene fibre and pulp produced desirable results as long as the amounts incorporated were below certain limits. The negative effects of fibres on compressive strength were less pronounced when the two fibre types were used in combination. The interactions between polyethylene fibre and pulp in deciding the specific gravity, volume of permeable pores and water absorption capacity of cementitious materials were either negligible or only moderately significant.