Physico-chemical properties are key starting points for risk assessments of chemicals. They provide a description of the chemical, and prove useful in assessment of environmental behaviour, uptake routes into organisms, toxicokinetics and ultimate effects in organisms. For nanomaterials, relevant physico-chemical properties can differ from those commonly considered for non-nanomaterials (e.g. surface area versus boiling point). With this in mind, The OECD WPMN has striven to develop tools that can assist in identifying appropriate physico-chemical parameters to better understand the link between those parameters and potential human health and environmental effects of nanomaterials, and to facilitate prediction of such effects. This report is intended to help in improving the conduction of the studies, in addition to promoting consistent data reporting (including reporting details on sample preparation and measurement protocols) to maximise utility and comparability of the data.