10 is provided with a metal housing 12 usually of stainless steel surrounding a bundle 14 of individual compacted layers 16 to retain the layers 16 in alignment the housing 12 is provided with marginal overfolded lips 18 the lips 18 prevent movement of the individual layers 16 in response to the pulsing of the engine in for example an internal combustion engine the layers 16 are as indicated above corrugated thin metal which when laid up one on top of the other would normally nest together and 34 blind 34 the module and prevent the transmission of gas e g exhaust gas therethrough as shown in fig1 the corrugations are in the form of a regular triangular pattern as above indicated they could be in any geometric pattern e g sinusoidal square wave trapezoidal waves or modified triangular waves in which the apices are rounded off to relieve stress examples of such wave forms are illustrated in the co pending application of wesley p bullock and william a whittenberger entitled 34 nonnesting straight corrugation metal foil and method for making same 34 now u s pat no 4 810 588 the corrugated foil layers 16 are maintained in spaced relation by the interposition of a fiber or a bundle of fibers 20 looped around the ends and between the successive layers 16 these fibers or threads 20 restrain the otherwise normally nesting foil layers 16 against nesting and blocking the.