I've been using this rope caulk for a few years now and it's great! Dirt cheap too!
(Click any pic to enlarge)
It comes in a roll like this........

And I use a wodden wall paper roller (the kind used to do the edges when hanging the paper) to smooth it and create trasitions in rail height easily.

It's flexible, and stays that way for many years, so it's quiet, and it's very easy to work with.

I can lay dozens of feet of it in just minutes, and since it's just a little tacky, it stays where I put it with no further adhesive. Ballast and scenery will hold it in place when all is said and done. I pull it apart lengthwise for N scale widths, for HO just use it straight from the package.

This was all layed in about ten minutes and is ready for track.



(This shows with the track installed, but it was part of that which went down in about ten minutes. Obviously, the track took longer. The cheap latex caulk I use to secure the track sticks to this stuff well too.)

I don't know if this is what you're talking about, but it works for me!