Coating two surfaces with polymer brushes has been shown on many occasions to reduce friction by orders of magnitude. These ultra-low frictions are believed to stem from be the very low level of interpenetration between confined brushes. We have recently developed a surface force style apparatus that allows direct measurements of the structure of polymer layers under confinement using neutron reflection. We propose to use this setup to study the interpenetration of two poly(ethylene oxide) (PEO) brushes in aqueous solution. We will bring together two PEO brushes, identical except that one will be deuterated and one hydrogenated. This will allow us to measure their interpenetration in detail, we will vary both the grafting density of the brush and the applied confining pressure. This proposal has the potential to greatly benefit our understanding of the brush mediated ultra-low frictions.