What do I use to fill my gaps?

[Elsacosplay]

For the non-armored gaps, such as major joins and such. I've seen people use like a plastic dryer vent material like this -> http://img.weiku.com/waterpicture/2011/10/27/6/Aluminum_Foil_ventilation_pipe_Vent_Hose_634578381952134384_5.jpg

But I'm really unsure about if that's what I need exactly or how to even get a hold of something super wide for it to be usable. Or is another alternative that works better?