Foam

I do like the ergonomics of that knife. The only drawback I see is blade changing, not as easy as snap offs. I don't have any Homasote to cut, but I have a lot of fiberboard, and the better grip may be worth the inconvenience.

Great tip!!!...Thanks for sharing....I just extended my layout by 4 feet and will be cutting some homasote soon...and I do remember all that dust last time.. 

Easiest and cleanest cutting of Homasote that I have done was with a bandsaw and you can put a 45 degree bevel on the edges for your roadbed.

Thanks for the tip, Tom. Harbor Freight's  "Oscillating Multi Tool" also works great too on homosote and foam insulation. It pretty much vibrates it way through and cuts like butter with very little dust.

I too am working on my roadbed and am just about done.  I guarantee that you can cut Homasote with a power tool in your living-room with absolutely no dust.  Simply install a blade cutting knife in your Saber or hand held power jig saw.  You can even tilt the blade to 45 degrees, but you need to only cut in one direction.   Right to left or Left to right, depending on the angle tilt.

I find that with both a hand held blade knife or one in your power tool, frequent blade changes are required.  While the hand tool is easiest just to replace he blade, I end up hand re-sharpening the power tool blade once it appears to take a little more pressure to cut.

When using the power tool, be careful not to overheat the blade.  It isn't difficult to get it so hot you can't hold on to it.  It is also easier to bend when hot.  So don't force it.  This is especially true when cutting at a 45 degree angle and you fail to keep the bottom plane of the angled blade flat against the Homasote.  I believe you get so used to holding the power tool square to the Homasote when in normal use, you forget that it is the 45 degree plane that really needs to be flat.  In other words, when cutting at a 45, there is a tendency to tip the handle up as if you were cutting a straight cut.  This can bend a hot blade.

I have also made my own blades for the saber saw by grinding or power sanding off the teeth of a standard blade.  I file after, apply 600 grit paper and then stone a new edge.  The reasoning here is that when a blade breaks, it is tough to have to drop everything and run to the Hardware store.

I just couldn't cut all my roadbed by hand and the power saw with blade installed is just the ticket.  

Thanks...