The original RASCO system used filters made from PVC fly screen mesh wound around a centre core and encapsulated by an outer sleeve. This method of trapping odours onto flyscreen was a tried and tested method taken from the trials in South Africa in the 90s for the detection of landmines and is still used in Europe today.
REST filters are made in the UK from a porous fibre material encapsulated in a plastic bar-coded sleeve and placed in an airtight security-sealed container. They are less labour-intensive to manufacture and work in exactly the same manner as the original RASCO filter.
They are made under controlled conditions, to ensure the quality and consistency of the filters.