The method of Borel resummation is used to obtain an accurate representation of renormalization-group functions of the n -vector model within the minimal renormalization scheme. This permits to relate the nonuniversal critical behaviour of different quantities well away from criticality. The results can be used to estimate the range of applicability of the n -vector model. Application to the λ-transition of 4 He explains the measured effective exponent of the superfluid density along the λ-line.