Remoulded polyurethane (PU) foam is used in crash mats for sports activities such as indoor climbing walls and high jumping, and in dry ski slope padding. The response of such a PU foam was measured under impact strain rates. Finite Element Analysis (FEA), with the foam modelled as a hyperelastic compressible material, was used for the evaluation of an impact of a headform on crash mats of a range of thicknesses. The predicted headform forces were underestimated by about 35%, compared with data from instrumented headform drop tests, because of limitations in modelling a viscoelastic material with an air compression contribution. FEA can be used to design mats to avoid head injury if the impact velocity is known. Allowance must be made for the variability of the foam properties.

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Polyurethane (PU) chip foam was characterised for air flow resistance, using a modification of the BS 4443 method, and for compressive impact response. A finite difference model was developed for the air flow in the impacted foam, including the effects of strain on foam permeability. It successfully predicted a non-uniform stress distribution across foam block of diameter > 100 mm, and showed that air flow is responsible for some but not all the hysteresis in this distribution for impact velocities > 3 m/s. Air pressure measurements, made in narrow vertical cavities inside impacted blocks of the foam, confirm the air pressure contribution to the total stress.