3D pen filaments explained: PCL, PLA and ABS

The filament is the pen's fuel, and its safety system

Every 3D pen does one thing: it melts a strand of plastic and pushes it out of a nozzle so the melted line can be drawn and cool into a solid shape. That means the plastic chooses the temperature, not the pen. A material that softens at 60 degrees C allows a cool-running pen. A material that needs 200 degrees C demands a hot one, whatever the box says about who it is for.

This is why the filament question and the safety question are the same question. When our safety guide says the surface temperature is the number that matters, the filament is the reason that number is what it is. So before comparing colours and pack sizes, it is worth two minutes on what these three plastics actually are.

PCL: the low-temperature material made for children

PCL, short for polycaprolactone, is the material children's pens are built around, and its defining feature is a remarkably low melting point: the plastic softens and flows at around 60 degrees C. Because the pen only needs to reach that modest temperature, everything the child interacts with can stay far cooler than in any other pen category. It is the single property that makes a true kids' 3D pen possible.

How cool the touchable surface actually gets still varies from maker to maker, which is why verification matters. Pen'Up's pen, running its own PCL, has a surface temperature of 35 degrees C verified in a laboratory, which is skin-warm and carries no risk of burns in normal use. Other kids' pens on PCL run higher at the surface while remaining genuine children's products. The material makes the low-temperature category possible; the engineering and the verification decide where in that category a pen sits.

Beyond the temperature, PCL suits children well in the hand: it flows smoothly, hardens quickly enough to build with, stays slightly flexible rather than shattering, and produces very little smell in use. Pen'Up's version is the Fil'Up range: PCL made for the pen, on 10 metre spools of 1.75 mm strand, in a wide range of colours, available at penup3d.com.

PLA: a fine material, for hotter machines

PLA is the everyday plastic of the adult 3D printing world, a plant-derived material that prints crisply and holds detail well. It is a perfectly good plastic. It is simply not a children's plastic, because PLA does not melt at anything like PCL's temperature: pens and printers built for it run vastly hotter, and the generic high-temperature pen category that uses PLA and ABS operates at roughly 200 to 300 degrees C at the nozzle.

A device in that range is a workshop tool. In the hands of a supervised teenager or an adult it makes strong, precise parts, and there is nothing wrong with it in that role. The problem is only ever the pairing: a nozzle hot enough to melt PLA is hot enough to injure a child instantly, and no feature list compensates for that. If a pen's specifications say PLA, it belongs on a teenager's desk at the earliest, not in a toy box.

ABS: tougher parts, higher heat, stronger smell

ABS is the plastic of car dashboards and classic building bricks: tough, rigid and durable. In the pen world it sits at the far end of the same high-temperature category as PLA, needing even more heat to flow, and it brings one extra characteristic worth knowing: heated ABS releases a noticeably stronger smell, which is why adult makers use it in well-ventilated spaces.

For a parent the conclusion is short. ABS produces impressively durable results in experienced hands, and it has no place anywhere near a child's pen. If durability for a kids' project matters, a solidly drawn PCL piece is more than sturdy enough for keyrings, decorations and repaired toys, without a hot nozzle in the house.

The three materials at a glance

Temperatures describe material categories, not any specific branded product. The high-temperature figures refer to the generic PLA and ABS pen category as a whole.

Sticks, spools and the 1.75 mm rule

Within the kids' PCL world, filament arrives in two forms that do the same job: short pre-cut sticks fed in one at a time, or longer lengths wound on a small spool. Spools mean fewer reloads mid-project, which children appreciate once builds get ambitious; Pen'Up's Fil'Up refills take the spool approach, with ten metres of strand per spool.

The measurement that is not negotiable is the diameter. Almost every kids' pen is built around a 1.75 mm strand, and the feed mechanism grips that size and no other. A thicker strand jams at the entry; a thinner one slips in the motor and feeds erratically. Material right, diameter right, made for your pen: those three checks are the whole compatibility story, and our refills guide turns them into a buying routine with costs and pack sizes.

Why you should not mix and match

The temptation arrives about a month in: the starter filament is running low, and an online marketplace offers a rainbow bundle of mystery strands for a few euros. Our advice is to leave it in the basket, for three reasons.

• Safety was tested as a system. The CE compliance and EN71 testing behind a good kids' pen apply to the pen running its intended filament. An unknown plastic changes the melting behaviour and takes the pen outside everything it was tested for.
• Clogs and damage. A strand that needs more heat than the pen produces does not melt properly; it smears, sticks and blocks the nozzle. Most of the jammed pens behind our troubleshooting guide started with the wrong strand.
• Quality is invisible until it is not. Even genuine PCL varies in consistency. Cheap strands can feed unevenly, snap in the mechanism and vary in diameter along their own length.

The saving is small and the downside is the pen. Filament made for the pen keeps the safety, the warranty and the smooth afternoon intact.

Questions parents ask