The Dirzepo filter is the 8th object approved by the S.C.M. (Servizio Chimico Militare, chemical military service) on 20 February 1935. A derivative of this filter, named Dirzepest, was used in Hungary.
The Dirzepo was the civilian variant of the T.35 filter, varying only in the colour being light orange, the upper collar being some times slightly different and the markings, which showed the name and in some cases the S.C.M. license too. The filter contains a layer of particulate filtering material made of resin-impregnated wool and viscose rayon at the bottom and a layer of activated charcoal, pumice and other blocking substances at the top. Before being opened, the bottom intake is covered by a small sheet of waxed canvas and the top is closed using a 40 mm lid, with all of this bound with a string closed using a small lead seal. After the filter has been opened for the first time, it could be closed again using the 40 mm lid and a small rubber seal attached through a string to the filter.
It was made in two variants, depending on the manufacture date. Early Dirzepo filters had a slightly elevated collar and simple markings, while the latest ones were identical in shape to the T.35 filters and had more information in the marking.It was bought alongside any S.C.M. licensed mask when the dedicated filter expired or when there was no dedicated filter at all.