A flat flexible hose for transporting a fluid, in particular a garden hose for transporting water, comprising: - at least one first inner layer defining an axis; - at least one second layer; - at least one reinforcement textile layer interposed between said at least one first layer and at least one second layer; wherein said at least one first inner and one second layer ( 2, 3) and said at least one reinforcement textile layer cooperate mutually so that the flexible hose is susceptible to move between an inoperative position in which it is substantially flat-shaped and an operative position in which it expands radially to take a substantially tubular shape, the hose moving from the inoperative position to the operative position under the pressure of the transported fluid and from the operative position to the inoperative position when the pressure of the fluid pressure ceases; wherein said at least one first inner and one second layer ( 2, 3) are respectively made of a first and a second thermoformable polymeric material, mutually compatible with each other, said first and second polymeric material having elastic behaviour both in said inoperative position and in said operative position of the hose; wherein said at least one reinforcement textile layer consists of rigid textile yarns which at least partially have a respective first and second predetermined inclination ( α, β) opposite each other with respect to said axis, said rigid textile yarns of said at least one reinforcement textile layer further holding the radial expansion of the hose in said operative position, substantially preventing the widening thereof starting from the latter position; characterized in that said at least one reinforcement textile layer is a knitted layer with chain stitches of the tricot type with rows of stitches and courses of stitches, at least one of said rows of stitches and courses of stitches consisting of said chain stitches, the hose being free of at least one braided and/or spiralled reinforcement textile layer. - at least one first inner layer defining an axis; - at least one second layer; - at least one reinforcement textile layer interposed between said at least one first layer and at least one second layer; wherein said at least one first inner and one second layer ( 2, 3) and said at least one reinforcement textile layer cooperate mutually so that the flexible hose is susceptible to move between an inoperative position in which it is substantially flat-shaped and an operative position in which it expands radially to take a substantially tubular shape, the hose moving from the inoperative position to the operative position under the pressure of the transported fluid and from the operative position to the inoperative position when the pressure of the fluid pressure ceases; wherein said at least one first inner and one second layer ( 2, 3) are respectively made of a first and a second thermoformable polymeric material, mutually compatible with each other, said first and second polymeric material having elastic behaviour both in said inoperative position and in said operative position of the hose; wherein said at least one reinforcement textile layer consists of rigid textile yarns which at least partially have a respective first and second predetermined inclination ( α, β) opposite each other with respect to said axis, said rigid textile yarns of said at least one reinforcement textile layer further holding the radial expansion of the hose in said operative position, substantially preventing the widening thereof starting from the latter position; characterized in that said at least one reinforcement textile layer is a knitted layer with chain stitches of the tricot type with rows of stitches and courses of stitches, at least one of said rows of stitches and courses of stitches consisting of said chain stitches, the hose being free of at least one braided and/or spiralled reinforcement textile layer.