Impregnation of a preformed network of nanofibrils leads to high fibre volume fraction nanocomposites and with this good mechanical properties have been achieved. However, comparing nanofibrils composite made with different volume fractions and different matrices is difficult. In order to do this, and in doing so gain insight into the most promising approaches, methods of measuring reinforcing efficiencies are being developed. The results show that for matrices with low stiffness the stiffness reinforcing efficiency is high. However with high fibre volume fraction and high stiffness, this network effect may lead to a lack of exploitation of the properties of the nanofibrils. Alignment of the nanofibrils is also a key in effective reinforcement. In addition, upscaling of the impregnation process requires a good understanding of permeability and adaptation of existing permeability models for cellulose nanofibrils networks as well as experiments on their permeability are ongoing.