Is it any good ?

I watched a clip the other day of someone making buildings out of polystyrene - the expanded foam rather than Styrofoam extruded foam.

He used a hot knife to mark out the stones but not sure what the backing for the polystyrene was.  It's pretty delicate stuff but, from his clip, made some nice stone walling etc.

Has anyone used the material and if so, how difficult is it to handle, does it need coating with something to toughen it up  and is it durable on a layout ?

I made these bridge supports from polystyrene, I just carved the lines with a knife. Not sure what kind of styrene it was but once I painted it with acrylic it hardened up when it dried. ( it’s a replica of mumps bridge in Oldham, it was knocked down to make way for the tram station)

Is that expanded polystyrene or extruded Graham ?  Ordinary package type polystyrene or styrofoam type material ?

It was some sort of packaging material. Not sure what type it was, but it’s not that crumbly stuff. It’s quite firm and easy to carve with a craft knife. 
Another option is the florists foam block (the grey one not the green) and once it’s painted it’s ok. 

I think the florist foam is called oasis. 

Ah, OK - Oasis is a completely different product.  Oasis is phenolic foam, not polystyrene.

The "firm" packaging foam you mention is probably "extruded" polystyrene commonly known as "Styrofoam" (XPS) whereas the softer white (usually) stuff which results in thousands of statically charges "balls" if cut is "expanded" polystyrene (EPS).  This latter EPS can also be very hard but is very easy to tell apart from XPS.

I think the bridge I made on the great train robbery was styrofoam xps, I cut it to shape and carved it. Then I painted it. 
The mumps bridge I made in this thread was the grey florists foam block. It’s easy to work with and once painted it seems to have a firm finish to it. 

Look up Kingspan insulation panels. Find a local building site or someone doing an extension, ask if they are using it and so can you get some offcuts. It has a foil outer ' skin' which you can peel off and the inner foam core is quite dense and great for carving

Extruded Foam XPS is available to buy specifically for modelling, but as Matt says, off cuts of insulation panels probably won't cost anything.

SM SunniMix 5 PCS Foam Board Hobby Foam High Density DIY Model Material blue Sheet for Crafting, Modeling, Sculpture, diy for Crafts 30cm x 20cm x 2cm : Amazon.co.uk: Home & Kitchen

White XPS craft foam


 

Either type will blunt knives. Use a hot wire cutter or hot-pointed probe. I use an old soldering iron set at a low temperature. Expanded doesn't take kindly to sanding, but extruded does. However, you might get some pointed questions about pink or blue dust going everywhere.

If the smooth surface of the extruded type is gently scored and then rattle-can sprayed, the solvent etches along the score lines. I have never tried it with stonework or setts, but it gives great plowed fields.

I’ve used several different types of foam, I used a bread knife to cut mine and a disposable craft knife for intricate bits. I’ve seen the soldering iron technique on YouTube, it’s trial and error but you’ll find a method that suits yourself.