A matrix for exchanging heat between a first fluid and a second fluid, in particular for an air-oil application in a turbine engine, includes an envelope defining a flow path of the first fluid and a network extending into the flow path and in which the second fluid flows. Along the axis defined by the curvature of the matrix, the dimensions of the envelope vary circumferentially (T(A)) and radially (R(A)). The matrix may be used with a heat exchanger.