Nearly half of the total energy generation in the developed world is inefficiently used to heat, cool, ventilate and control humidity in buildings. Unfortunately, the concepts developed through many research and demonstration projects have struggled to become assimilated into main-stream construction. In Europe, the most successful passive design standard, the German PassivHaus standard, has certified only 30,000 buildings in 15 years. Comparing this with the UK Government's 2016 target for the construction of 240,000 new homes per year and current quarterly output of around 29,380 homes it is evident that additional routes to achieving low and zero energy buildings must be investigated and developed if deep cuts in energy use and associated carbon emissions are to be attained by the building sector. Furthermore, there must be a focus on whole-life impact. To achieve the space heating energy targets of the PassivHaus standard, walls typically require insulation to a thickness of at least 300 mm and this level of conventional insulation material significantly increases the embodied energy content of the finished building. At present, inorganic insulation materials dominate the building industry, although interest in the use of natural fibre insulation products is steadily increasing. In Europe inorganic fibrous materials, e.g. stone wool and glass wool, account for 60% of the market. Organic foamy materials such as expanded and extruded polystyrene account for 27% of the market, whilst all other materials combined make up less than 13%. In the case of the mineral fibre materials adhesives are often added as are water-repellent oils as both increase mechanical strength. Expanded and extruded polystyrene are both oil-based polymerised polystyrol and the production process requires blowing agents which, since the phase-out of ozone depleting materials, are typically pentane and carbon dioxide, respectively. Pentane contributes to smog and ground level ozone and carbon dioxide, due to its low solubility and high diffusivity in polymers, make it difficult to produce low density foams which result in poorer thermal performance compared with those insulation materials made using HCFC blowing agents. Natural fibre insulation (NFI) can be seen as an excellent form of carbon emission mitigation. NFI not only reduces the in-service carbon emissions of buildings through reduced energy demands, but through the use of plant based fibres carbon is stored within the material, as a result of plant photosynthesis, so significantly reducing the global warming impact of the insulation material. However, much is unknown about the performance of NFI materials. Where evidence-based data are available they are almost universally based on steady-state test performance data rather than the more complex dynamic variations experienced in real buildings. Frequently, where test data relating to thermal conductivity are presented, it is based on standard test conditions of a material in a dry state and at one mean temperature. Accordingly practitioners use such test results for prediction of in-service energy performance or evaluation of retrofit benefits, often without consideration for variability due to the changeability in the thermo-physical properties of the material or the validity of the test conditions. Whilst this situation affects all building materials attempts have been made to evaluate sensitivity and the impact on energy performance for more conventional products but there is little evidence of the same approach for NFI. Furthermore, the hygroscopic nature of NFI materials results in much greater variability in their thermal performance. The primary aim of this project is the quantification of the dynamic thermal performance of NFI materials through experiment and simulation, which will help to support a growing 'green economy' and provide valuable data for building designers and developers of building simulation models.