As it is a thermoplastic material it has excellentthermal ductility, making it highly flexible and thussuitable for a variety of applications. Furthermore, manyof the varieties manufactured are ideal for representingglass and other transparent building elements. Theirsurfaces can be modified, for example satin matt effectscan be achieved by grinding acrylic glass with fine-grain sandpaper, and grid structures and patterns can beproduced by milling, grooving or scoring acrylic glasswith a sharp blade. Whilst the number of different typesof plastic may be too exhaustive to discuss in detail here,the main criteria for the application of plastic in a modelshould be the form and colour desired and its surfaceproperties. It is worth expanding on the most commontypes used in modelmaking:
1 Cast acrylic sheet
– Tends to have slight variationsin thickness. Consistent all round shrinkage (no morethan 2%) if at all. Can be easily re-worked when hot. Castacrylic is usually slightly cheaper than extruded acrylicand widely preferred for basic model construction.
2 Extruded acrylic sheet
– Thickness varies minimalor not at all. Potentially has irregular shrinkage overtime or heat exposure. Much more heat resistant thancast acrylic. Extruded acrylic is slightly more expensivethan cast and is usually used for more robust projectrequirements due to its heat resistance.
3&4 Rods, tubing and formed strip
– Made with thesame varied specifications as described above, there is alsoa wide range of shaped and sized strip sections available.These can be used to create forms on façades or asstructural elements and easily bonded to plastics.
5 Ureol/model board/chemi (chemical) – wood/resinboard
– This modelling board was brought to the marketunder the name Ureol although it is known by severalnames in the manufacturing and design industry.This man made polyurethane based board is widelyused in product prototype development due to its highquality finish when machined. It is also easy to refinethrough sanding and polishing and lends itself to thestresses that can be asserted through CNC routing ormilling processes. In architectural modelmaking it canplay a valuable role in the creation of block model masterplans that often involve the repetition of block buildingstyles. Strips can be easily shaped and individual blocklengths cut to suit a given scale with minimum finishingrequired. Although considered to be quite an expensivematerial choice, the finishing time saved due to itshigh quality finish is often the deciding factor for theprofessional with a tight time scale for production.Ureol is available in a number of different colours.These colours are not intended to be aesthetic but serveas in indication of its chemical properties. Each colourindicates the density of the board with lighter colourshaving the lowest.
