There are many iterations of foam: rigid, plain styrofoam sheets, extruded, and expanded. The afterwards two, extruded and expanded, are probably the most popular when it comes to home building projects, but what’s the difference?
Expanded Often called Beadboard, sheets are created from sound beads of polystyrene. These beads are expanded by injecting and dissolving handful of pentane gas in to the base material during production. Under heating, the gas expands the beads to form shut cells. These cells approx are. 4o times the quantity of the original bead, and can get molded to create insulation boards, blocks, or shapes. While a closed cell structure and resistant to water nonetheless, it isn't as resistant to wetness as XPS is, but that could be splitting hairs. It is generally cheaper than it ‘extruded’ cousin and scientific tests have shown EPS to possess a lower result on the environment and can be recycled easier than XPS.
Extruded, this foam begins with solid polystyrene crystals. The crystals, and also other additives are fed into an extruder. Within the extruder itself, high pressure and heat form the mixture into a plastic fluid. This thick liquid plastic is then forced right into a die where it emerges and expands to a foam. This foam is then shaped, cooled, and cut. Due to the extrusion process, XPS is able to maintain steadily its thermal and/or physical properties more uniformly than EPS and makes an excellent replacement for corrugated cardboard, thus it gained in attractiveness amongst architectural modelers. Another benefit of XPS is undoubtedly it’s strength: because it put through higher compression during the manufacturing process, it is more rigid than EPS slightly. Also, as the closed cell structure is indeed finer than that of EPS, XPS resists wetness better. I assume once this became the defacto amongst these modelers, it migrated over to railway modelers. Manufacturers add dye often, which has no effect on the XPS apart from identification of the manufacturer.
So which is better? Well, after reading numerous articles it does indeed seem that Extruded foam includes a few slight positive aspects after all. But i want to note the focus on slight. For most railway modelers with simple layouts, there probably is no difference because the foam will be covered anyway by other materials such as for example plaster. In the end, it appears the three main variations are: Expense, where EPS gets the advantage; Strength, where XPS stacks up a bit better and retains its rigidity, and finally, Moisture resistance, where once more, XPS has a minor advantage.
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