Plate for a heat exchanger, intended to be positioned between a first and a second adjacent plate in a stack, the plate comprising: - an octagonal main panel having two first opposite junction sides (101a, 101b), two second opposite junction sides (102a, 102b) and four support sides (100a-100d), the main panel comprising a first face and a second face, opposite to the first face, - eight panels (11a, 11b, 12a, 12b, 20a-20d) connected by folding lines to the main panel, including: -- two first junction panels (11a, 11b), each first junction panel extending from a first respective junction side (101a, 101b) and being suitable for being connected to a second junction panel (12a, 12b) of the first adjacent plate in order to define a first duct for circulation of fluid, -- two second junction panels (12a, 12b), each second junction panel extending from a second side (102a, 102b) and being suitable for being connected to a first junction panel (11a, 11b) of the second adjacent plate in order to define a second duct for circulation of fluid distinct from the first duct for circulation of fluid, and -- four support panels (20a-20d), each support panel extending from one of the support sides (100a-100d) and being suitable for being connected to a support panel (20a-20d) of the first adjacent plate in order to maintain the plates with respect to each other in stack, wherein each support side (100a-100d) of the main panel extends between a first adjacent junction side (101a, 101b) and a second adjacent junction side (102a, 102b) of the main panel, and wherein the first junction panels (11a, 11b) are folded towards the first face of the main panel and the second junction panels (12a, 12b) are folded towards the second face of the main panel. - an octagonal main panel having two first opposite junction sides (101a, 101b), two second opposite junction sides (102a, 102b) and four support sides (100a-100d), the main panel comprising a first face and a second face, opposite to the first face, - eight panels (11a, 11b, 12a, 12b, 20a-20d) connected by folding lines to the main panel, including: -- two first junction panels (11a, 11b), each first junction panel extending from a first respective junction side (101a, 101b) and being suitable for being connected to a second junction panel (12a, 12b) of the first adjacent plate in order to define a first duct for circulation of fluid, -- two second junction panels (12a, 12b), each second junction panel extending from a second side (102a, 102b) and being suitable for being connected to a first junction panel (11a, 11b) of the second adjacent plate in order to define a second duct for circulation of fluid distinct from the first duct for circulation of fluid, and -- four support panels (20a-20d), each support panel extending from one of the support sides (100a-100d) and being suitable for being connected to a support panel (20a-20d) of the first adjacent plate in order to maintain the plates with respect to each other in stack, -- two first junction panels (11a, 11b), each first junction panel extending from a first respective junction side (101a, 101b) and being suitable for being connected to a second junction panel (12a, 12b) of the first adjacent plate in order to define a first duct for circulation of fluid, -- two second junction panels (12a, 12b), each second junction panel extending from a second side (102a, 102b) and being suitable for being connected to a first junction panel (11a, 11b) of the second adjacent plate in order to define a second duct for circulation of fluid distinct from the first duct for circulation of fluid, and -- four support panels (20a-20d), each support panel extending from one of the support sides (100a-100d) and being suitable for being connected to a support panel (20a-20d) of the first adjacent plate in order to maintain the plates with respect to each other in stack,