There are a large number of plastic filaments used in 3D printers that use “material extrusion” to print 3D objects. Material extrusion is any 3D printer that builds up a 3D object, layer by layer, by melting a material from a computer controlled nozzle. The most common extrusion material is plastic, or more precisely, thermoplastics. Thermoplastics allow a very precise control of the melting point of the material, so they can easily be controlled by a computer. The filament is the plastic thread, or wire that is typically on a spool that feeds into the extrusion head of the 3D printer. This filament can be made of an ever-changing assortment of plastics. The two most common forms of plastic are ABS and PLA.
ABS is Acrylonitrile Butadiene Styrene, a petroleum (oil) based thermoplastic that is used in industry for injection molded parts. LEGO bricks are a good example of ABS plastic.
PLA is polylactic acid, a bio-degradable from of plastic that is manufactured from plants such as corn starch or sugar cane. It is a common polyester available by synthetic alteration of naturally occurring lactic acid.
ABS plastic has a much higher melting point than PLA, and is also stronger and harder. It has a longer lifespan than PLA. ABS is made from oil, so its manufacture is much more damaging to the environment. It is not suitable for any printed objects that come in contact with food. When a 3D printer uses ABS, the printed object can have a tendency to deform when not printed on a heated bed. Ventilation is recommended when the printer is in use since the fumes given off when the plastic melts contain low-level hazardous materials.
PLA is much more environmentally friendly since it is a bioplastic and not derived from oil. It can be completely recycled. The printed object is slightly smoother in appearance when PLA is used. PLA can be printed on a cold surface without deforming, so a printer does not need a heated bed. No harmful fumes are released when printing with PLA. A printed object made with PLA is less sturdy than an object made from ABS, and can deform if left in a very warm environment. Printing with PLA can typically be done at a higher speed.
In summary, if you are looking to make plastic parts for a machine, ABS is the best choice because it is strong, has a long lifespan, and a higher melting point (so the part can operate in a warm environment without deforming). If you are making plastic parts for art purposes or models for display, PLA is the best choice because its easier to print, has a desirable appearance, doesn’t release harmful fumes when printed and overall is better for the environment. Another point to note is that PLA can be in contact with food, but cannot be put in a dishwasher as it will deform from the heat.