3D printers use a process called Fused Deposition Modeling (FDM for short).  FDM is a process by which a thin strand of plastic is forced through a hot nozzle (aka extruded) and deposited on a flat surface.  The model itself is built up in horizontal layers like a layer cake – each layer on top of the one below it. 

At room temperature all of the different kinds of plastics, called “filaments”, are solid.  As you apply heat they become more pliable until eventually they melt completely.  The point at which they melt is critical and is different for each type of plastic.  Not only is the melting point important but also the maximum temperature that can be used.  Too cold and the filament won’t melt and can’t be extruded.  Too hot and it will flow like water, not deposit properly and may also begin discolor.  It’s important to keep the filament in the correct temperature range.to avoid either of these problems.  There are many different types of plastics that can be used in a 3D printer.  There are exotic materials like Carbon Fiber or even Wood (!), but let’s stick with the basics – PLA, PETG and ABS.

When choosing the filament material to use several factors come into play. I’ve listed them in the order I consider them in, but you may decide a different order is appropriate for you.

Application – Is the part going to be used indoors or outdoors?  Will it be in direct sunlight, under the hood of a car, etc?

Strength – Mechanical strength must be sufficient for the intended application

Cost – Some filaments are more expensive than others, and some are VERY expensive

Color – Not all filaments come in all colors

Difficulty – Some filaments are more difficult to print than others and may require special equipment

Knowing how the part will be used is going to determine which filaments are good candidates.  A  part that’s used indoors in a cool environment that isn’t mechanically stressed could use any filament.  A part that sits on the dashboard of a car in the sun in the summer in Arizona will need something very different.  Once the choice of filament has been narrowed down based on application we can move on to strength.  What kind of mechanical strength does the part need?  Does it just sit there (like a statue) or does it need to be “strong” (like a crank handle)?  After answering that question we are likely down to one or two filaments, so of course we’ll choose the cheapest UNLESS color is more important than cost.  Generally speaking PLA comes in more colors than PETG, and PETG comes in more colors than ABS.

PLA stands for Polyactic Acid.  It’s made from renewable sources like sugarcane and corn starch and is used in the food industry for food containers and plastic films.  The fact that it’s renewable (and cheap) makes it a popular filament in the 3D printing industry.  PLA “sticks well” to the printing surface.  Combined with its low melting temperature this filament is considered “easy to print” and is a common choice for beginners.  Because of its relatively low melting point (around 374 degrees Fahrenheit)  PLA is best for indoor applications and not in direct sunlight.  It’s also best for applications that require medium to low mechanical strength.  You can buy PLA blends with excellent mechanical strength, such as PLA CF, but it is more expensive than “standard” PLA and requires special equipment.

So lets rank PLA:

Application – Indoors and not in direct sunlight

Strength – Low to medium

Cost – $

Color – Many!

Difficulty – Low

PETG stands for Polyethylene Terephthalate Glycol and is created using a chemical process.  PETG is commonly used for food containers and liquid beverage bottles and is recyclable.  It’s a bit more expensive than PLA but also comes in many colors.  PETG has a higher melting point (446 degrees Fahrenheit) than PLA which makes it suitable for outdoor/direct sunlight applications.  It’s “UV stable”, meaning that it will fade very little over time and will not lose mechanical strength because of exposure to UV light (sunlight) and has high mechanical strength.  

Application – Indoors/outdoors, direct sunlight

Strength – Medium High to High

Cost – $$

Color – Many!

Difficulty – Medium

ABS stands for Acrylonitrile Butadiene Styrene and is created using a chemical process.  ABS plastics are commonly found in harsh environments such as the plastics under the hood or your car.  It has high mechanical strength and high UV resistance.  It will not fade or lose mechanical strength over time as a result of being exposed to sunlight and of the 3 filaments discussed here it is the “toughest”.  ABS has a higher melting point (482 degrees Fahrenheit) than PETG which not only lends to its heat resistance but also makes it the most challenging to print.  As ABS cools it shrinks much more than PETG or PLA which can result in warped parts.  As such ABS is best printed in a temperature controlled chamber, although for smaller parts this may not be required.  ABS also tends to come in fewer colots than PLA or PETG, with white or black being common.

Application – Indoors/outdoors, direct sunlight, harsh environments

Strength – High

Cost – $$ – $$$

Color – Some, but not nearly as many as PLA or PETG

Difficulty – Medium to High

Hopefully this helps you understand the 3 most common materials and the pros and cons of each!

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