The tensile response of some simple fibre assemblies is calculated, using the actual stress-strain relationships of constituent fibres. These stress-strain relationships are obtained by a scaling procedure, with distributions of ultimate tensile properties and an average stress-strain curve as input. Two polypropylene fibres with different polydispersity index, but the same weight-average molecular weight and draw ratio, are considered in this article. The fibre with the narrowest molecular weight distribution (MWD) has about 30% higher average strength. On the other hand, if bundles with a large number of fibres are compared, the strength of a bundle consisting of fibres with narrow MWD is less than 10% higher. The maximum strength of a random planar distribution of fibres is 36% and 44% of the average fibre strength, for fibres with narrow and broad MWD, respectively. The strength of a chain-of-bundles decreases as the number of bundles increases, and as the number of fibres in each bundle decreases. When the number of bundles is large, the strength of a chain-of-bundles containing fibres with broad MWD exceeds that of a chain containing fibres with narrow MWD. The assemblies considered in this article illustrate effects in real assemblies, such as non-woven fabrics. They also provide references for the tensile properties of real assemblies.