I don’t care for cork. I think it is way to high for most applications so I am considering buying a roll of polyethylene foam floor underlayment and using it as a blanket on the plywood ( sorry I don’t buy into the styrofoam is great group). Then after the track is layed and pinned but before ballasting cutting out the areas where there is no track Has anybody tried this? any results? In the past I have used cheap paneling cut in 1" strips but this might be quiter and is about the same thickness.
Pick up truck hop cap tape works well. Cheap too!
The bulk of the model railroaders use either cork or an equivalent thickness material for good reason…to achieve a near-prototypical roadbed height for mainlines and some spurs. In some instances, two layers of cork are used to replicate UP, BNSF & other RR mainlines passing through certain geographic regions requiring the extra height because of flooding, unstable ground and other natural effects that may interact with the right-of-way. A switching layout or logging operation may not require something as thick as cork in certain situations.
Paneling?? It’s lamination is too dense to push a track spike through. You could glue the track to it but cardboard (boxes or shirtbacks) would be cheaper and easier to use.
Many of us choose extruded foam (not the beaded styrofoam) because it is so easy to use. You can cut it with a knife, hot wire or jigsaw and it won’t chunk off in pieces like the FBC. You can glue stuff to it and also “grow” trees by merely pushing the trunk bases into it.
I used the FBC 2" Quadlam foam backed carpet for 2-rail O scale with great success to reduce noise but it cannot be cut without chunking and virtually nothing will adhere (glue) to it. If you accidently touch it with a hot wire gun, the fumes are very toxic.
I eventually decided to use it strictly for roadbed and nothing more. Be advised that heavier locomotives tend to waiver back and forth because it is not as dense as the extruded foam. It was originally designed to be used as a gymnastic mat and the surface deflection per square cm is significantly greater than most model railroading materials.
I’d get a sample swatch a few feet long and mess with it for awhile. It’s not bad stuff but I think the model RR community would have been using it a lon
I am using flooring underlayment. Poly stuff, not the older sponge type. It’s about 1/8" thick. My layout is flat and I just rolled the stuff out, taped the edges together and put down the track. I have nailed the track down through the underlay. This is the quietest running RR I have ever encountered. Much quieter than my old homasote based layout.
I first thought that I should glue the stuff down along my pre-drawn lines and I tried that with my hot glue gun. The glue melted through the underlay pretty quickly so I stopped doing that and just didn’t bother fastening the stuff down by itself. As it turns out, there is no need. I haven’t done any ballasting yet and I know that this will make a difference in the sound level but there you go. I’m sure I’ll be able to live with it.
I think this stuff is great! Here’s a photo of where I was when I last took pics…
Tayder…The FBC I used appears to be totally different from what you’re using. So based upon what you’ve said and how well it appears in the nice accompanying photo, I may have to check it out over at the local building supply store.
Ahhh…I guess I should have mentioned that I was replying to ndbprr’s question 
LOL! But anyway, I like the way this stuff performs so far!