The words between you and a part that works.

56 terms, each with a definition that stands on its own and a line on what it changes when you print. Nothing here invents a number.

01 / 10 terms

Materials

Polymer names are the first thing you meet and the easiest thing to misread, because the same acronym is sold at ten different qualities.

Filament

A thermoplastic strand of constant diameter, wound on a spool, that feeds an FDM printer.

The two standard diameters are 1.75 mm and 2.85 mm, and they are not interchangeable. Diameter tolerance matters more than brand: a strand wandering by ±0.05 mm changes how much plastic leaves the nozzle, and the surface shows it.

PLA

Polylactic acid — the easiest filament to print, stiff and accurate, but it loses stiffness above roughly 55 °C.

It is the right answer for form, fit and finish, and the wrong answer for anything that sits in a car or in the sun.

PETG

Glycol-modified polyethylene terephthalate — it bends instead of snapping, shrugs off water, and prints without a chamber.

In exchange it wants slower speeds than PLA and dry filament. Stringing in PETG is almost always a moisture signal rather than a temperature one.

ABS

Acrylonitrile butadiene styrene — more heat resistant than PLA or PETG and easy to finish, but it shrinks hard as it cools.

Anything with a footprint over roughly 80 mm warps or splits without a warm enclosure. ABS releases styrene while printing, so ventilation is a requirement, not an option.

ASA

Acrylonitrile styrene acrylate — essentially ABS with the butadiene replaced, which is what lets it survive UV.

Print settings are nearly identical to ABS. If the part goes outside choose ASA; if it stays indoors and only needs heat resistance, ABS is cheaper.

TPU

Thermoplastic polyurethane — a flexible thermoplastic that prints parts which bend, grip and seal.

Selected by Shore hardness, not by feel. TPU wants a short, tightly constrained filament path; a direct-drive extruder is close to a requirement on the softer grades.

Nylon (PA)

Polyamide — a family that slides, survives fatigue and resists brittle failure, used for gears, hinges and wear parts.

The most hygroscopic family in the catalogue: nylon takes on water in hours rather than weeks, and wet nylon loses up to a third of its tensile strength. This family lives and dies by drying discipline.

Polycarbonate (PC)

The strongest common filament: high heat deflection, high impact energy, and optically clear if you want it.

It demands a 300 °C hot end, a chamber and a dry spool. Printed below 260 °C the layers do not fuse, and the part delaminates under exactly the load you bought PC for.

Fibre-reinforced composite (CF, GF)

A base polymer filled with chopped carbon (CF) or glass (GF) fibre to raise stiffness and cut warping.

Stiffer is not tougher: fibre raises modulus but lowers elongation at break, so the part resists bending and then fails more suddenly. The fibre abrades brass in tens of hours, so a hardened nozzle is required.

Photopolymer (resin)

A liquid that hardens under UV light, used by MSLA and DLP resin printers.

Uncured resin is a skin sensitiser and an aquatic toxin: nitrile gloves, ventilation, and nothing down the drain. Cured resin is inert.

02 / 14 terms

Properties and standards

Every number on a data sheet is the result of one specific test. Knowing the test is knowing what the number speaks about — and what it says nothing about.

Tensile strength

The greatest stress a specimen carries while being pulled along its axis until it breaks, in MPa.

Measured to ISO 527 for rigid plastics and ISO 37 for elastomers, on a flat-printed (XY) specimen, so the figure is in-plane strength. Very few real parts fail in pure tension — if yours bends, read flexural strength instead.

Tensile modulus

Stiffness: the ratio of stress to strain in the elastic region, in MPa.

This is the number that answers “will it flex”, while tensile strength answers “will it break”. Two different questions, and a material can be good at one and poor at the other.

Elongation at break

How many percent longer the specimen gets before it breaks.

It is the proxy for brittle versus tough. A few percent means the material shatters without warning; a few hundred means it deforms first. Living hinges and snap fits need this number high, not tensile strength high.

Flexural strength and modulus

Resistance to bending, measured by resting a specimen on two supports and pressing in the middle (three-point bending), to ISO 178 or ASTM D790.

For brackets, mounts and covers — which is most functional printed parts — this is closer to reality than tensile strength.

Impact strength (Charpy, Izod)

The energy a specimen absorbs while being broken by a swinging pendulum, in kJ/m² or J/m.

Charpy (ISO 179) supports the specimen at both ends and strikes it edgewise; Izod clamps one end as a cantilever. On the same polymer the two give different numbers, and a notched specimen reads an order of magnitude below an unnotched one. Never compare Charpy against Izod.

HDT — heat deflection temperature

The temperature at which a test bar sags a specified amount under a constant flexural stress, usually 0.45 MPa or 1.8 MPa.

It is a comparison point between materials, not a maximum service temperature. A part under sustained load creeps below its HDT, and the higher test stress always gives a lower figure — so always read the condition next to it.

Vicat softening point

The temperature at which a needle of specified cross-section penetrates 1 mm into the specimen under a set load.

Vicat and HDT measure two different things and often differ by tens of degrees on the same polymer, so they do not substitute for one another.

Glass transition temperature (Tg)

The temperature range over which an amorphous polymer changes from hard and glassy to soft and rubbery.

Tg is why a PLA part sags in a parked car without ever approaching its melting point. For a part that gets warm, Tg is the real ceiling; nozzle temperature is irrelevant to it.

Shore hardness (Shore A / D)

Indentation hardness read on a durometer: the A scale for soft materials, the D scale for harder ones.

On a flexible grade this is the selection parameter. 95A prints on almost any direct-drive extruder and still bends; 85A squeezes like rubber but buckles in the extruder if you print it fast. Choose by how much the part must deform, not by how soft it sounds.

Density

Mass per unit volume in g/cm³, measured to ISO 1183.

This is the number that turns spool weight into filament length, and the volume in your slicer into grams you have to pay for. It therefore sits underneath every cost calculation.

Hygroscopic

The property of absorbing and holding water from the surrounding air.

Absorbed water flashes to steam in the nozzle, which shreds the extrusion and leaves popping, stringing and a foamed surface. At the humidity Vietnam holds for most of the year, this is the single most common cause of prints that go bad for no visible reason.

Anisotropy (Z strength)

An FDM part is far stronger in the plane of its layers (XY) than across them (Z).

Almost every data-sheet figure is measured on a flat-printed specimen, so they are XY values. Orientation is therefore a structural decision: place the part so load runs within the layers rather than across the bonds between them.

Creep

The slow, permanent deformation of a plastic held under constant load over time.

It is why a printed PLA clamp looks fine on assembly and has sagged three months later, at room temperature. No data-sheet figure tells you this — design sustained-load parts to a lower stress.

UV stability

A material's ability to keep its colour and its toughness under prolonged sunlight.

PLA chalks and goes brittle; PETG yellows and loses toughness. Among common filaments, ASA is the one designed for sustained exposure.

Printer and settings

The words in the slicer and on the printer's spec sheet. Most print problems are fixed here rather than by changing spool.

FDM (fused deposition modelling)

A process that extrudes molten plastic as beads and stacks them layer by layer.

Part strength depends on how well those beads weld together almost as much as on the polymer. Temperature, speed and cooling are therefore structural settings, not cosmetic ones.

MSLA / DLP (resin printing)

Processes that cure a layer of liquid resin at a time with 405 nm light through an LCD panel (MSLA) or a projector (DLP).

The whole layer is exposed at once, so print time depends on part height rather than on how many parts are on the plate. In-plane resolution is set by the panel, not by the software.

Nozzle

The tip at the end of the hot end whose bore shapes the extrusion; its diameter sets the width of the printed bead.

0.4 mm is the default. Go to 0.6 mm for load-bearing parts and for fibre-filled material: thicker beads, fewer layers, fewer weak points. Go down to 0.2 mm only when you genuinely need features smaller than that.

Hardened nozzle

A nozzle in hardened steel or with a ruby tip, for abrasive materials.

Carbon fibre, glass fibre and even the mineral filler in matte PLA abrade brass. The bore goes oval and flow control disappears — usually before you work out why.

Hot end and high-flow hot end

The heated assembly that melts filament before extrusion; a high-flow version has a longer melt zone so it can push more plastic per second.

Print speed is limited by melt throughput, not by how fast the motors can move. Setting 300 mm/s on a standard hot end just produces an under-extruded part.

Direct drive and Bowden

Two extruder layouts: direct drive puts the feed motor on the hot end, Bowden puts it further away and pushes filament down a tube.

For flexible material the difference is decisive: the free length of filament inside a Bowden tube compresses and buckles instead of arriving at the nozzle. 85A TPU on Bowden is barely worth attempting.

Enclosure (chamber)

A closed shell around the build area that holds the air temperature high and steady through the print.

Not to keep the part warm but to slow the shrinking: lower layers that cool more slowly build less stress between layers, and the part neither warps nor splits. For ABS, ASA and PC it is a requirement, not an accessory.

Layer height

The thickness of each printed layer, typically 0.08 to 0.32 mm on an FDM printer.

Thinner layers give a smoother surface but not a stronger part — more layers means more bonds. Around 75 % of the nozzle diameter is usually the good balance between time and strength.

Infill

The internal lattice inside a part, set as a percentage and a pattern.

Adding perimeters buys far more strength than adding infill percentage for the same plastic. Past roughly 40 %, more infill mostly buys print time and weight.

Retraction

Pulling the filament back a short distance while the head travels without printing, so plastic does not ooze out.

It is the first setting people reach for when they see stringing, and usually the last one they should touch: with PETG and nylon, dry the spool and drop the temperature first.

Flow rate (extrusion multiplier)

A multiplier on how much plastic the slicer asks the printer to extrude, used to correct for the real machine and the real filament.

Calibrate it with a single-wall cube: print it, measure the wall with calipers, adjust to match. On a correctly assembled printer this is the single change that most improves surface quality.

Pressure advance / linear advance

Compensation for the pressure inside the hot end as the head accelerates and decelerates, so beads do not bulge at corners or start thin.

The faster you print, the more you need it. Without it every corner is fatter than the straight it belongs to, and that is a calibration fault rather than a material one.

Temperature tower

A tall test print divided into bands, each printed at a different nozzle temperature.

It is the only way to answer what temperature is right for your machine, with this spool, in this colour. The window on a spec sheet is where you start the tower, not the conclusion.

Brim, raft and skirt

Three helper structures printed around or under a part: a brim is a flat collar joined to its edge, a raft is a plate underneath it, a skirt is a free-standing outline that does not touch it.

A brim is the most effective of the three against warping because it holds the part's edge down. A skirt does nothing for adhesion — it primes the nozzle and lets you see first-layer height before the part begins.

Support

Temporary structure printed under overhangs so the plastic has something to land on, removed after printing.

Cheaper than support is the right orientation and an overhang under 45 degrees. On FDM every surface that touches support comes out worse than a free one — so put them where nobody looks.

Annealing

Holding a printed part below its melting point for a period to raise crystallinity and release internal stress.

It buys heat resistance and strength but shrinks the part, so print to the annealed dimension or design in the allowance. Many nylon data-sheet figures are annealed values; unannealed parts read lower.

Drying and dry box

Holding a spool below its glass transition for hours to drive water out, then printing straight from a heated sealed box so it cannot take the water back.

Too hot and the spool welds to itself and will not unwind. Each family has its own window, and for nylon this is a step before every print rather than a rescue.

04 / 8 terms

Print defects

Naming the defect correctly is half the fix. Each one below has a most-common cause, and it is usually not the first one you would guess.

Warping

Edges and corners lifting off the plate as the lower layers cool and contract.

Fix it with heat first and adhesion second: chamber heat, bed heat, cooling almost off for the first twenty layers, and only then a wide brim. With ABS and ASA, opening the enclosure mid-print is enough to cause it.

Stringing

Fine threads of plastic strung between parts of a print, left by ooze while the head travels.

The right order is: dry the spool, drop the nozzle 10 °C, and only then raise retraction. With PETG and nylon, moisture is the cause most of the time — tuning retraction on a wet spool only changes the shape of the defect.

Elephant foot

The first few layers bulging outside the design outline, leaving the base of the part flared.

Caused by a first layer squashed too close plus a bed running too hot. Fix it by recalibrating first-layer height, dropping the bed a few degrees, or applying elephant-foot compensation in the slicer — and it ruins fit tolerances before you notice it.

Layer shift

The whole upper part of a print offset sideways from the lower part, leaving a visible step.

This is a mechanical fault, not a material one: a loose belt, a pulley slipping on its shaft, or the head striking a warped part. Do not try to fix it with temperature.

Delamination

Layers separating along the layer plane, usually partway up a part.

It means the weld between layers was never strong enough: nozzle too cold, cooling too aggressive, or not enough chamber heat for an engineering material. It is also the plane a load-bearing part will fail along.

Under-extrusion

Less plastic leaving the nozzle than the slicer asked for, leaving gaps between beads and walls thinner than designed.

The most overlooked cause is a worn or partly blocked nozzle, followed by asking for more flow than the hot end can melt. Extrude into air and watch it before blaming the spool.

Clog

A blockage in the hot end or nozzle that stops the flow entirely or makes it intermittent.

A heat-creep clog happens when filament softens too high up the path — usually poor hot-end cooling rather than dirty filament. A clog that returns at the same point is a hardware signal, not a material one.

First-layer adhesion

The part failing to stick to the plate, or letting go partway through.

Three causes, in order of frequency: a plate with skin oil on it, the wrong first-layer height, and a bed temperature that does not suit the material. Washing the plate with dish soap and hot water fixes more cases than every adhesive combined.

05 / 7 terms

Resin printing

MSLA has its own vocabulary: exposure instead of temperature, peel force instead of bed adhesion.

Exposure time

The number of seconds each resin layer is lit at 405 nm to cure it.

It is the most important setting on a resin printer, and it depends on the resin, its colour, the layer thickness and even the age of the LCD panel. Over-exposure loses fine detail and embrittles the part; under-exposure stops layers bonding.

Bottom layers

The first few layers, exposed far longer than the rest so the print grips the build plate.

Over-exposed bottom layers are a common cause of elephant foot on resin prints and of parts that will not come off the plate. It is its own setting, not a multiplier on normal exposure.

Lift speed

How fast the build plate is raised off the FEP film after each layer.

Lifting faster raises peel force: a part with a large flat cross-section tears off its supports or stretches the FEP. Lifting slowly is the time you pay for a print that finishes.

FEP film

The clear film stretched under the resin vat that light passes through and the print peels off.

A consumable: once it is cloudy, scratched or stretched, your calibrated exposure is no longer correct. A run of failures after weeks of stability usually points at the film rather than the resin.

Suction force and hollowing

The vacuum created as the plate lifts a print off the FEP; hollowing the model and adding vent holes is how you reduce it.

A hollow model without a vent is worse than a solid one: the sealed cavity traps resin and pulls harder. Tilt the model 20–30 degrees so each layer's cross-section is smaller.

Wash and cure

The two mandatory post-processing steps of resin printing: washing off uncured resin in isopropyl alcohol, then curing under UV.

Over-curing is a real failure mode: parts yellow and go brittle. Start short and add time only if the surface stays tacky. Most resin property figures are post-cured values — green parts are far weaker.

Burnout (investment casting)

Firing a plaster mould so the wax-loaded resin pattern burns away completely, leaving a cavity for molten metal.

The deciding figure for a castable resin is the ash left after burnout: ash is a defect in the cast metal. That is why castable resins are published by wax content and ash residue rather than by tensile strength.