A method of fabricating a three-dimensional object, the method comprising sequentially forming a plurality of layers in a configured pattern corresponding to the shape of the object, thereby forming the object, wherein forming at least one of said layer comprises: (i) dispensing by at least one inkjet printing head at least one modeling material formulation, said at least one modeling material formulation comprising: an unsaturated cyclic monomer polymerizable by ring opening metathesis polymerization (ROMP); a catalyst or a catalyst system comprising a catalyst for initiating ROMP of said monomer; a curable material polymerizable by free-radical polymerization (FRP); and a curing agent (or system) for initiating free radical polymerization of said curable material; (ii) exposing said at least one modeling material formulation to a condition for inducing initiation of ROMP of said monomer by said catalyst; (iii) maintaining said formulation at a first temperature for a first time period; said first time period being such that at least 80 % of said unsaturated cyclic monomer undergo polymerization by said ROMP during said first time period, and (iv) subsequent to said first time period, exposing the modeling material formulation to a condition for inducing initiation of free-radical polymerization of said curable material by said curing agent, said condition for inducing initiation of said free radical polymerization comprising a second temperature, wherein said second temperature is higher than said first temperature and wherein said second temperature is higher than said first temperature, and wherein said curing agent is a thermally-activatable curing agent that is activated at said second temperature, to thereby obtain a cured modeling material in said layer. (i) dispensing by at least one inkjet printing head at least one modeling material formulation, said at least one modeling material formulation comprising: an unsaturated cyclic monomer polymerizable by ring opening metathesis polymerization (ROMP); a catalyst or a catalyst system comprising a catalyst for initiating ROMP of said monomer; a curable material polymerizable by free-radical polymerization (FRP); and a curing agent (or system) for initiating free radical polymerization of said curable material; an unsaturated cyclic monomer polymerizable by ring opening metathesis polymerization (ROMP); a catalyst or a catalyst system comprising a catalyst for initiating ROMP of said monomer; a curable material polymerizable by free-radical polymerization (FRP); and a curing agent (or system) for initiating free radical polymerization of said curable material; (ii) exposing said at least one modeling material formulation to a condition for inducing initiation of ROMP of said monomer by said catalyst; (iii) maintaining said formulation at a first temperature for a first time period; said first time period being such that at least 80 % of said unsaturated cyclic monomer undergo polymerization by said ROMP during said first time period, and (iv) subsequent to said first time period, exposing the modeling material formulation to a condition for inducing initiation of free-radical polymerization of said curable material by said curing agent, said condition for inducing initiation of said free radical polymerization comprising a second temperature, wherein said second temperature is higher than said first temperature and wherein said second temperature is higher than said first temperature, and wherein said curing agent is a thermally-activatable curing agent that is activated at said second temperature, <EOS>