The Cool Blue solid colour effects filter gives a steelier blue effect than the Blue filter. Cool Blue filters give cool tones to skies. It is available in 3 densities, 1,2 and 3. Different colour filters can be used in combination together or with graduated colour or neutral density filters to create interesting bespoke effects. This 67mm filter is usable with Hitech 67mm holder systems or any 67mm (2.67″) holder. The filter is also available in 85mm, 100mm, 150mm and 165mm sizes. Hitech filters are made from the highest quality 1.5mm optical resin.