A multi-ply expandable filter media formed of obliquely oriented honeycomb organized into a ply or run having expandable honeycomb cells with one run oriented at, preferably an acute angle, of 30.degree. to 60.degree. relative to the cells of an adjacent run. Preferably, the respective plys or runs are arranged in relative parallel planes defining a planar space therebetween. There is provided means for collapsing the filter media into a closed compressed, transportable state, and when ready for use as a filter media, to allow the same to be expanded and pulled open and to be constrained in an preselected, open, expanded position so that the cross-sectional area of each cell is thereby substantially increased. In this manner, the juxtaposed, open plys allow directional change for airflow flowing through the filter media, encouraging deposits of air-borne material to become attached to the wall surfaces of the family of cells of each run or ply. To enhance adhesion, an adhesive may be sprayed over the cell walls.

Unexpanded structural honeycomb material formed of permanently creasable material is extended in its expansion direction and compressed perpendicular to the expansion direction, e.g. between pressure rollers, so that the cells adopt a configuration in which they have dimensions in the expansion direction which are large compared with their dimensions in the direction of compression and the creasable material is creased. On subsequently being allowed to expand, the material adopts a self-sustaining open cellular configuration.

A honeycomb structure comprising at least one main honeycomb structure 10 and sub-honeycomb structures 21, 22 axially disposed, in series, on both end surfaces of the main honeycomb structure 10. Partial plugs 15 are constituted for some of the cells 11 of the main honeycomb structure 10 by facing the intersecting portions of partitioning walls 211, surrounding the cells of the sub-honeycomb structure 21 disposed adjacent to the main honeycomb structure with some of the cells of main honeycomb structure, and the arrangement of the partial plugs 15 at one end surface 101 of the main honeycomb structure differs from that at the other end surface of the main honeycomb structure 10.

An adsorption filter includes at least one thin plate honeycomb filtering medium carrying a gas-adsorbing medium thereon and a filter case housing the honeycomb filtering medium therein. The thin plate honeycomb filtering medium is disposed in the filter case in such a manner as to make a series of V configurations with respect to a ventilation direction.

A paint arrestor for absorbing paint overspray comprises a series of layers of sheet material, each of the layers being slit and expanded to define an array of air spaces distributed in columns. The air spaces alternate in size from column to column and repeat in size in every other column. Means are provided for securing the layers in contiguous, overlying relationship with one another.