Embodiments of the present invention include methods and devices for trapping particulate matter suspended in exhaust from, for example, automotive diesel engines. Particulates carried in exhaust are actually a colloidal suspension of finely divided particulates in a fluid (in this case, the exhaust gases). This colloidal mixture is channeled through an open spiral exhaust channel. The particulates will differentially tend to travel through the fluid in a straight line, which leads them to collide with a fine mesh or porous material that defines the open spiral exhaust channel. The gas, on the other hand, will easily traverse the spirally shaped exhaust channel, with its molecules bouncing around the curved path of the spiral. Continuing through the device, more and more particulates will build up in the surrounding meshwork or porous material.