I build layouts and dioramas using the standard white foam (Expanded Polystyrene, EPS) that you can get in any hardware store. This type of foam is easy to work with and you can work with it inside the house. The only tool you need is basically a sharp knife, but a hot wire foam cutter of some sort is recommended.
Foam Sheet Goods from Woodland Scenics
About Standard White Foam
Standard white foam is also known as EPS (Expanded Polystyene). It is made from thousands of small beads that make up a sheet or block of foam. EPS insulation boards found at the hardware store are typically of poor quality because they are designed for insulation and not model building.
EPS comes in all sorts of other qualities and can be either cut or made in a mold depending on your requirements. EPS is also typically that white stuff that encapsulates your brand new television, IKEA furniture, or in some cases model railway locomotive.
Note: Another popular foam product is XPS (Extruded Polystyrene) or "pink foam". In Denmark, where I live, this type of foam is not available. That is why I went with the EPS instead.
My house does not have room for a workshop, and I do not like to do wood working inside the house. Foam makes it easy for me to have fun with my hobby without getting complaints from the girlfriend.
With the foam from the hardware store, I always have problems with the measurements. Keep in mind, that these sheets are made for insulation and not top-precision model building. They can easily be off by 2 mm, meaning that a 5 cm (1.9 inch) block might be 4,9 mm in one end and 4,5 mm in the other end. If you do not pay attention to this, your layout will not be level. 1 mm (0.03 inch) is a lot when the track height is code 83. Basically the height of a rail.
This made me think of the Woodland Scenics foam sheets. I always thought they were a bit pricy, so I never really considered them. I had never seen one in real life, because no store in my neighbourhood carries Woodland Scenics stuff. I always order it online.
Getting more and more frustrated about the foam from the hardware store, I ordered some of the Woodland Scenics sheets for comparison. And I must say, the Woodland Scenics foam makes a world of difference. It is much, much better quality than the foam from the hardware store, and it looks like it is made in a mold. The latter gives you precise measures, meaning that 1 inch is 1 inch every time. The foam sheets might seem pricy, but for a reason.
Here are some close up pictures for comparison. The lighting is a bit off, which makes the amount of beads visible. The first picture is of a piece of standard foam from the hardware store and the second is Woodland Scenics Foam Sheet Goods.
Notice that there are many more beads in the Woodland Scenics foam. The Woodland Scenics foam is also very robust. You cannot squeeze it with your fingers, where you are normally able to complete squeeze standard white foam.
Standard white foam from the hardware store. Very soft.
Woodland Scenics Foam Sheet Goods. Much more density and much easier to work with and cut. Very hard.
There is no doubt in my mind that the Woodland Scenics Foam Sheet Goods are much better quality than the foam from the hardware store. It also costs a lot more, but I think the price difference is worth it, if you are frustrated about all the extra work you have to do with the standard white foam.
If you are used to build with standard white foam, and a bit frustrated about the measurements being off, give Woodland Scenics Foam Sheet Goods a try. Or at least check them out the next time you visit the hobby store.