How to choose a filament material

What is filament actually made of, and why does that matter?

Filament is a plastic feedstock melted through a nozzle one thin layer at a time, and every common type is a different polymer with its own melting behavior, strength profile and weight. The material you choose changes how the part performs long after it is printed, not just how easy it is to print.

The two numbers that matter most before you buy a spool are density, which tells you how much a given volume of the material weighs, and nozzle temperature range, which tells you whether your printer and hotend can even run it. A part that looks identical in two materials can weigh differently and fail under completely different conditions.

When should I actually print in PLA instead of something tougher?

PLA has a density of about 1.24 g/cm3 and prints at 190 to 220 degrees Celsius, the lowest and most forgiving range of any common filament. It is the right default for indoor decor, prototypes, brackets that never see stress, and anything a beginner is dialing in a printer with.

Skip PLA for anything that sits outside, near heat, or under repeated mechanical load, since it softens at a relatively low temperature and is more brittle under sudden impact than the alternatives below.

When does PETG earn the extra print difficulty over PLA?

PETG has a density of about 1.27 g/cm3 and prints at 230 to 250 degrees Celsius. It genuinely resists water, tolerates noticeably more heat than PLA, and flexes rather than snapping under sudden stress, which is why it shows up in outdoor brackets, drainage fittings and parts that ride in a car.

The tradeoff is more stringing and a bond to bare PEI build plates strong enough to tear the sheet on removal, so plan on a thin release agent such as a glue stick when printing PETG on a bare PEI bed.

Is ASA really just weatherproof ABS, and is that the right way to think about it?

Yes, essentially. ASA has a density of about 1.07 g/cm3 and prints at 240 to 260 degrees Celsius, very close to ABS, but it adds real UV resistance that ABS lacks. An ABS part left outdoors will yellow and go brittle under sunlight over time; an ASA part is built specifically to resist that.

If a part is going outside for any length of time, such as a mailbox bracket or a garden fixture, ASA is the right call over ABS. If the part stays indoors, plain ABS at a lower cost usually covers the same strength and heat resistance without needing the UV additive.

When does a part actually need nylon or TPU instead of a rigid plastic?

TPU has a density of about 1.21 g/cm3, prints at 220 to 240 degrees Celsius, and is a flexible rubber-like material meant for gaskets, phone cases and parts that need to bend repeatedly without cracking. It is not a structural material and should not be chosen for anything that needs to hold a rigid shape under load.

Nylon has a density of about 1.14 g/cm3 and prints hot, at 250 to 280 degrees Celsius, and it delivers the best abrasion resistance and toughness of the common filaments, which is why it shows up in gears and load-bearing mechanical parts. Nylon absorbs moisture from room air faster than any other common filament, so it must be dried immediately before every single print, not just when it feels damp.

How much does the material change how much a spool actually weighs out?

Because filament is sold by weight, not length, a denser material gives you less printed volume per kilogram. PETG at 1.27 g/cm3 yields noticeably less usable length than PLA at 1.24 g/cm3 for the same 1 kg spool, and ABS at 1.04 g/cm3 stretches further than either. This matters when comparing spool prices across materials, since a cheaper spool of a denser filament can cost more per printed part than it first appears.

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