Suitable materials to line my duct silencers?

Hi, Just a quick question regarding the various materials which can be used to line duct silencers. I have observed people using 1" 703 fiberglass insulation, 1" RW3 rockwool, and commercial ductliner. I cannot get 703 in my part of the world ( or I can't get it at a reasonable price), I am also having trouble sourcing ductliner and i am not happy using rockwool wrapped in plastic as i have visions of it disintegrating over time. My question, Can i use regular acoustic foam for this application and if so, what should the spec ( density ) of the foam be and how thick should it be.... Any other thoughts or ideas for other materials I might be able to use would be appreciated... King regards hally

Hi again Hally! You should not use 703, or ordinary fiberglass, or ordinary mineral wool for that. You should use proper duct liner. Ductliner has a top layer or coating that keeps the fibers in place, which is very important. I would imagine that duct liner must available in Ireland: I guess there must be HVAC systems there somewhere! :) - Stuart -

Hi Stuart, Nice to talk again, hope all is well with u... yes duct liner is available here in Ireland but because hvac or ducted ventilation systems are not common place, it costs a fortune which i don't have. Is foam of a sufficient density and thickness a viable alternative? Thanks for ur input hally (GASPING FOR FRESH AIR)

Rigid fiberglass panels should generally not be used for this application, however, in a pinch, regular panels could be used if they are treated once in place with an application of shellac or varnish (usually applied as a spray - not thick enough to seal, just enough to ensure the fibers will stay in place - think hairspray).