Filaments and materials

In Chapter 2 you picked a printer. Now you need something for it to print with. That something is called filament, and choosing the right one matters more than almost any setting you will ever touch. A good part in the wrong plastic is a bad part. The squeezer we are building has to survive lemon juice (an acid) and warm soapy water (a cleaning), so the plastic is not a detail. It is the whole point.

This chapter explains what filament actually is, walks through the handful of materials a beginner needs to know, and tells you plainly which one we will use and why. No chemistry background needed. Every term gets explained the first time it shows up.

What filament actually is

Filament is a long, thin thread of plastic wound onto a spool, the way thread is wound onto a sewing reel. The printer pulls this thread in, pushes it through a small heated nozzle (the part that melts it is called the hotend), and lays the melted plastic down in thin lines that stack up into your object. When the plastic cools, it hardens back into a solid. That is the entire trick of FDM printing, which stands for Fused Deposition Modeling, a fancy name for "melt a thread and draw with it."

A few practical facts about the thread itself:

• Diameter. The thread comes in a precise width. Almost every desktop printer today uses 1.75 mm filament. A few older or larger machines use 2.85 mm (sometimes loosely called "3 mm"). The two are not interchangeable, so check your printer's manual and buy 1.75 mm unless you have a specific reason not to. When in doubt, 1.75 mm is the safe default.
• Spool size. Filament is usually sold by weight, most commonly a 1 kg spool (1 kilogram of plastic, not counting the reel it sits on). That is a lot of printing for a beginner. Your practice prints and one lemon squeezer will use a small fraction of a single spool.
• Rough cost. Plan on roughly $20 to $30 per kilogram for ordinary PLA or PETG (this is approximate and varies by brand, color, and where you shop). Specialty and "fancy finish" filaments cost more. The good news: one spool lasts a beginner a long time.

So when someone says "I print in PLA," they mean the spool of plastic thread they feed the machine is made of a material called PLA. Let me introduce the materials worth knowing.

The materials a beginner should know

There are dozens of filament types, but you only need to understand a few. I will describe each in plain terms, then put them side by side in a table.

PLA: the easy default

PLA (polylactic acid) is the friendliest plastic in 3D printing and the one almost everyone learns on. It is a plant-based polyester, often made from corn or sugarcane starch, and it is mildly biodegradable, but only under industrial composting conditions (high heat and the right microbes). It will not quietly rot away in your drawer or in a landfill, so do not treat it as disposable.

Why beginners love it: PLA melts at a relatively low temperature, sticks to the print bed easily, and barely warps. Warping is when a part lifts or curls off the bed as it cools, ruining the print, and PLA does this far less than other plastics. It is also stiff, meaning it holds its shape and feels rigid, which makes for crisp, clean prints.

Its weaknesses matter for our project. PLA softens in heat. Leave a PLA part in a hot car, run it through a dishwasher, or pour boiling water on it, and it can sag or deform. It is also more brittle than other plastics, meaning it tends to snap rather than bend when stressed. And it does not love sustained moisture or acid, which is exactly what a lemon squeezer faces.

Best for: learning, decorations, low-stress parts, prototypes, and all of your early practice prints. We will use PLA to learn on, not for the final squeezer.

PETG: tougher, and our squeezer plastic

PETG (the letters stand for polyethylene terephthalate, glycol-modified, but you can just say "PETG") is the next step up and the material we will print the lemon squeezer in. It is a close cousin of PET, the clear plastic used in disposable water and soda bottles, so it comes from a family of plastics already trusted around drinks.

Compared to PLA, PETG is tougher and slightly flexible, so it bends a little under stress instead of snapping. It handles heat better, so warm water will not deform it the way it might deform PLA. Most important for us, it resists moisture and mild acids like lemon juice far better than PLA does. It also takes warm soapy cleaning in stride.

The tradeoff is that PETG is a bit fussier to print than PLA. It prints hotter, it is prone to stringing (thin wispy strands of plastic left between parts of the print, like cobwebs), and it wants a well-tuned first layer so it sticks without being squished too hard. None of this is hard, it just means PETG rewards a little patience. We cover the settings in Chapter 5.

Why PETG is the squeezer choice. Our part has a specific job: squeeze lemons (acidic juice), then get rinsed in warm water and reused. That combination of acid contact, warm-water cleaning, and the need to hold up to repeated hand pressure is precisely where PLA falls short and PETG shines. PETG resists the acid, tolerates the warmth, and is tough enough to survive being squeezed and dropped. We spell out the design reasoning in Chapter 11 and the all-important food-safety caveats in Chapter 14. For now, just hold this thought: the squeezer is PETG.

ABS and ASA: strong, but skip them for now

ABS (acrylonitrile butadiene styrene) is the plastic in LEGO bricks and many appliance housings. It is strong and handles heat well. ASA is a close relative with better resistance to sunlight and weather, often used for outdoor parts.

Both are genuinely useful, and both are a headache for a beginner. They warp badly, so prints lift off the bed unless conditions are just right. They give off a noticeable smell and fumes while printing, so they really want an enclosure (a box around the printer that traps heat and contains the fumes) and good ventilation.

Honest recommendation: skip ABS and ASA while you are starting out. You do not need them for this project, and fighting warping on top of learning everything else is not a good first experience. Come back to them later if you ever need their heat resistance.

TPU: rubbery and flexible

TPU (thermoplastic polyurethane) is a soft, rubbery, flexible filament. Prints made from it bend and stretch like a phone case or a shoe sole. It is genuinely fun, and you could imagine using it later for a soft grip or a squishy seal on a project.

The catch is that flexible filament is harder to print. It has to be fed slowly, and on some printers (especially ones with the filament drive set far from the hotend) it can buckle or jam inside the machine.

Best for: later, once you are comfortable. Think of TPU as a "someday" material, not a first one.

Specialty filaments, in one breath

You will also see nylon (very strong and tough, but very moisture-hungry and tricky), wood-filled and carbon-fiber-filled filaments (PLA or PETG with particles mixed in for looks or stiffness, but they grind down brass nozzles over time), and exotic blends with metal powders or other additives. These are advanced or specialty materials. Note that they exist, then set them aside. Not now.

The comparison table

Here is the short version, honest and simplified. "Ease of printing" is from a beginner's chair, where higher is easier.

Don't be confused. PLA and PETG are both common, both come on 1 kg spools of 1.75 mm thread, and both are beginner-reachable, so people mix them up. The simple rule: PLA is the easy practice plastic; PETG is the tougher, more water and acid resistant plastic you use for parts that have a job to do. We learn on PLA and we build the squeezer in PETG. (Separately, do not confuse FDM filament printing with resin printing, which uses a liquid cured by light. That is a different machine and a different material entirely, and it is not what this book uses.)

Moisture: the invisible problem

Here is something nobody tells beginners until a print goes wrong: plastic filament absorbs water out of the air. The plastic is technically "hygroscopic," which just means it slowly soaks up humidity over days and weeks, especially in a damp room.

Why you should care: wet filament prints badly. When water-laden plastic hits the hot nozzle, the trapped moisture flashes into steam. You hear faint popping or crackling, you see extra stringing and rough, bumpy surfaces, and the finished part comes out weaker and uglier. It can take a perfectly good spool and make it print like junk.

PETG is fairly thirsty, and nylon is extremely thirsty (it can absorb enough moisture to print poorly in a single humid afternoon). PLA is more forgiving but not immune.

How to keep filament dry:

• Store sealed. Keep spools in an airtight container or a zip-top bag with a packet of desiccant (those little silica-gel beads that come in shoeboxes and absorb moisture). Many people use a dry box, which is just a sealed plastic tub with desiccant inside, sometimes with a hole so the filament can feed straight into the printer while staying sealed.
• Dry wet filament. If a spool has already gone damp, you can dry it: a dedicated filament dryer (a small warming appliance) or a low oven on a gentle setting will bake the moisture back out over several hours. Follow the temperatures your filament maker recommends so you warm it, not melt it.
• Buy what you will use. Filament that sits open for a year is filament slowly going stale.

You do not need a fancy setup on day one. A big zip-top bag and a couple of desiccant packs will protect your spools just fine while you learn.

Colors and finishes (and one honesty note)

Filament comes in every color, plus finishes that change how the surface looks: matte (flat, no shine, hides layer lines well), silk (glossy and shimmery), glow-in-the-dark, translucent, color-shifting, and more. These finishes come from extra ingredients mixed into the base plastic: pigments for color, additives for sheen or glow.

This leads to a caveat that matters a lot for a lemon squeezer, so read it carefully. The colorant and additives in a given spool are not automatically food-safe, even when the base plastic could be. A spool can be PETG (a polymer family used in food packaging) and still contain a pigment or additive that was never tested or rated for food contact. "PETG" on the label tells you the base polymer. It does not certify the dye, the additives, or the spool's manufacturing as safe for something your lemon juice touches.

So please do not read this chapter as "PETG is food-safe, done." It is not that simple, and overclaiming here could mislead you into trusting a part you should not. The real story (what food-contact actually requires, why a 3D-printed surface is tricky regardless of plastic, and how to think about it honestly) gets its own full chapter. See Chapter 14 before you let any printed part near food you intend to eat.

Takeaways

• Filament is a 1.75 mm thread of plastic (sometimes 2.85 mm on older machines) wound on a spool, usually 1 kg, melted and drawn by the printer's hotend. Budget roughly $20 to $30 per kilogram (approximate).
• PLA is the easy, stiff, low-warp plastic for learning. It is brittle and softens in heat, so it is wrong for hot, wet, or acidic jobs.
• PETG is tougher, slightly flexible, more heat resistant, and stands up to moisture and mild acids like lemon juice. It is a little fussier to print (stringing, first-layer tuning), and it is the plastic for our squeezer.
• ABS/ASA are strong and heat resistant but warp and fume; skip them as a beginner. TPU is rubbery and useful later but harder to print now. Nylon and filled or exotic filaments are advanced; not now.
• Learn on PLA, print the squeezer in PETG. That one sentence covers most of your early decisions.
• Keep filament dry. Wet plastic pops, strings, and prints weak. Store sealed with desiccant; dry a spool that has gone damp. PETG and especially nylon are moisture-sensitive.
• Color and finish additives are not automatically food-safe even on a food-family polymer. Do not overclaim; read Chapter 14 before any printed part touches food.

You now know what to load into the machine and why. Next we get our hands on the printer itself: leveling the bed, loading that first spool, and watching plastic turn into an object.

👉 Continue to First setup and your first print.