Particulate matter emitted from internal combustion engines has been shown to be harmful to human health, and is also damaging to the environment. Recently, legislation has been introduced that limits both the mass and number of particulate emissions that an engine may produce. To meet the new legislation, future gasoline vehicles will be need to be fitted with a filtration system similar to that already used on diesel vehicles, but known as a gasoline particulate filter (GPF). Differences in gasoline and diesel combustion products mean that these new GPFs need to be optimised for key properties such as low pressure drop combined with high particulate filtration and catalyst activity. One of the main challenges with GPFs is characterising and measuring global particulate distribution after it is trapped on the filter. Neutron tomography can be used to see and measure these particles.