Blade for a rotor of a rotary wing aircraft, which blade is intended to rotate about an axis of rotation, said blade extending along a blade axis between a blade root which is connectable to a hub of said rotor and a blade tip located at a free end of said blade and said blade extending along a transverse axis, which is perpendicular to said blade axis, between a leading edge and a trailing edge, said blade comprising a profiled portion located between said blade root and said blade tip, said profiled portion being made up of a series of aerodynamic profiles, each aerodynamic profile being located in a transverse plane, which is substantially perpendicular to said blade axis, and delimiting a cross-sectional area of said blade, said blade tip being located at a distance equal to a rotor radius R of said axis of rotation, a maximum distance between said leading edge and said trailing edge in said transverse plane constituting a chord c for said aerodynamic profile of said cross-sectional areas of said blade, an average chord c being an average value of said chord c over said profiled portion, a first forward direction being defined from said trailing edge to said leading edge and a second backward direction being defined from said leading edge to said trailing edge, said blade having a combination of laws of variation of the chords and of the twist, said twist being formed by the angular variations between said aerodynamic profiles of said blade, said chord increasing between the start of said profiled portion and a first cross-sectional area located at a first distance from said axis of rotation of between 0.6R and 0.9R, said chord decreasing beyond said first cross-sectional area, and said twist decreasing between a second cross-sectional area located at a second distance from said axis of rotation of between 0.3 R and 0.4 R and said blade tip, a first slope of said twist being between -25°/ R and -4°/ R between said second cross-sectional area and a third cross-sectional area located at a third distance from said axis of rotation of between 0.4R and 0.6R, a second slope of said twist being between -25°/ R and -4°/ R between said third cross-sectional area and a fourth cross-sectional area located at a fourth distance from said axis of rotation of between 0.65R and 0.85R, a third slope of said twist being between -16°/ R and -4°/ R between said fourth cross-sectional area and a fifth cross-sectional area located at a fifth distance from said axis of rotation of between 0.85R and 0.95R, a fourth slope of said twist being between -16°/ R and 0°/ R between said fifth cross-sectional area and said blade tip, said laws of variation of the chords and of the twist being combined with a law of variation of the sweepback, said sweepback, which is the angle between said leading edge and said blade axis, being directed towards the front of said blade between said start of said profiled portion and a ninth cross-sectional area located at an eleventh distance from said axis of rotation of between 0.5R and 0.8R, said leading edge forming a first front sweepback angle (α 1) with said blade axis that is strictly greater than 0° and less than 10°, said sweepback being directed towards the front of said blade between said ninth cross-sectional area and a tenth cross-sectional area located at a twelfth distance from said axis of rotation of between 0.6 R and 0.95 R, said leading edge forming a second front sweepback angle (α 2) with said blade axis of between 1° and 15°, said first front sweepback angle (α 1) being different from said second front sweepback angle (α 2), said sweepback being directed towards the back of said blade between said tenth cross-sectional area and said blade tip, said leading edge forming a third backward sweepback angle (α 3) with said blade axis of between -35° and -15°, characterized in that said twist varies piecewise linearly between two adjacent cross-sectional areas from said second, third, fourth and fifth cross-sectional areas (S2, S3, S4, S5) and between said fifth cross-sectional area and said blade tip, said first slope of said twist being less than said second slope of said twist, said second slope of said twist being greater than said third slope of said twist, said third slope of said twist being less than said fourth slope of said twist.