An absorbent article comprising: a cover layer; a barrier layer; an absorbent system arranged between said cover layer and said barrier layer; wherein said absorbent article has a thickness of less than 2.5 mm; and wherein at least a portion of said absorbent article satisfies one of the two following equations: AI > 2.37 − 0.77 ln BW / MCB, where BW/MCB is ≤ 5.9; and AI > 1.0, where BW/MCB is > 5.9. wherein MCB = Modified Circular Bend Stiffness; BW = Basis Weight of the Article; and AI = Absorbency Index, wherein AI = 6.27 − R 6.12 + 499 − FPT 495; wherein R = Rewet Value; and FPT = Fluid Penetration Time; and wherein the Modified Circular Bend Stiffness, the Basis Weight, the Rewet Value, and the Fluid Penetration Time are measured using the methods described in the description; wherein (i) when AI > 1.0, where BW/MCB is > 5.9 said absorbent system is substantially entirely SAP, wherein said SAP has an absorbent capacity of at least 20 g/g after 1 minute, and a total capacity of at least 40 g/g; wherein said SAP is secured by adhesive; and wherein said SAP has a gel blocking ratio of at least 0.50; and (ii) when AI > 2.37 - 0.77 ln(BW/MCB), where BW/MCB is ≤ 5.9, said absorbent system includes a material containing a mixture of from 90% to 40% cellulosic fibers and 10% to 60% of superabsorbent polymer. a cover layer; a barrier layer; an absorbent system arranged between said cover layer and said barrier layer; wherein said absorbent article has a thickness of less than 2.5 mm; and wherein at least a portion of said absorbent article satisfies one of the two following equations: AI > 2.37 − 0.77 ln BW / MCB, where BW/MCB is ≤ 5.9; and AI > 1.0, where BW/MCB is > 5.9. wherein MCB = Modified Circular Bend Stiffness; BW = Basis Weight of the Article; and AI = Absorbency Index, wherein AI = 6.27 − R 6.12 + 499 − FPT 495; wherein R = Rewet Value; and FPT = Fluid Penetration Time; and wherein MCB = Modified Circular Bend Stiffness; BW = Basis Weight of the Article; and AI = Absorbency Index, wherein AI = 6.27 − R 6.12 + 499 − FPT 495; wherein R = Rewet Value; and FPT = Fluid Penetration Time; and wherein the Modified Circular Bend Stiffness, the Basis Weight, the Rewet Value, and the Fluid Penetration Time are measured using the methods described in the description; wherein (i) when AI > 1.0, where BW/MCB is > 5.9 said absorbent system is substantially entirely SAP, wherein said SAP has an absorbent capacity of at least 20 g/g after 1 minute, and a total capacity of at least 40 g/g; wherein said SAP is secured by adhesive; and wherein said SAP has a gel blocking ratio of at least 0.50; and (ii) when AI > 2.37 - 0.77 ln(BW/MCB), where BW/MCB is ≤ 5.9, said absorbent system includes a material containing a mixture of from 90% to 40% cellulosic fibers and 10% to 60% of superabsorbent polymer. (i) when AI > 1.0, where BW/MCB is > 5.9 said absorbent system is substantially entirely SAP, wherein said SAP has an absorbent capacity of at least 20 g/g after 1 minute, and a total capacity of at least 40 g/g; wherein said SAP is secured by adhesive; and wherein said SAP has a gel blocking ratio of at least 0.50; and (ii) when AI > 2.37 - 0.77 ln(BW/MCB), where BW/MCB is ≤ 5.9, said absorbent system includes a material containing a mixture of from 90% to 40% cellulosic fibers and 10% to 60% of superabsorbent polymer.