Fix Brittle Prints: An Engineer’s Verdict on PLA vs. PLA+

Every week, a new client walks into my factory with a familiar story. They hold up a shattered plastic part, beautifully printed but broken clean in two, and say, “I don’t get it. I printed this in PLA+, the strong stuff. Why did it fail?”

My answer is always the same. I pick up two pieces of filament from my desk—one standard PLA, one a brand of PLA+ I trust. I bend them both. The standard PLA bends a little, then with a sharp snap, it breaks. The PLA+ bends further, turning white with stress, and continues to deform long before it finally tears.

“That,” I tell them, “is the entire story.”

The confusion around PLA and PLA+ (also called PLA Pro) is one of the biggest sources of frustration—and costly failures—in the world of desktop 3D printing. It’s a problem born from brilliant material science clouded by opaque marketing. To make an informed engineering decision, you need to understand what that “+” actually means, and more importantly, what it doesn’t.

For those who need the answer now, here’s the bottom line:

But this table, as useful as it is, doesn’t tell the whole story. It doesn’t explain why PLA+ can survive a hammer blow while standard PLA will shatter like glass. To understand that, we need to go back to basics.

The Foundation: What is Standard PLA?

Before we can add a “plus,” we have to understand the baseline. Polylactic Acid (PLA) is the undisputed king of hobbyist and professional 3D printing, and for good reason. It’s a thermoplastic polyester derived from renewable resources like corn starch or sugarcane. In our world, it’s the material we use for first-pass prototypes, architectural models, and anything where visual fidelity is more important than mechanical performance.

Think of a raw, uncooked strand of spaghetti. It’s very stiff and strong if you try to pull it apart (high tensile strength). But if you bend it even slightly, it snaps without warning. This is called brittle failure, and it is the defining characteristic of standard PLA.

This brittleness comes from its semi-crystalline molecular structure. It’s rigid, which is great for printing sharp details and avoiding the dreaded “warp” that plagues other materials. It also has a low glass transition temperature (Tg)—the point at which it turns from a hard solid into a rubbery state—of around 60°C (140°F). This is why it’s so easy to print (it doesn’t require a heated bed or enclosure) and also why you should never leave a PLA part in a hot car.

So, standard PLA is:

• Easy to print: Forgiving, low warp, no toxic fumes.
• Stiff and strong (in tension): Great for static, load-bearing parts.
• Brittle: Has almost zero impact resistance.
• Low temperature resistance: Don’t leave it in the sun.

It is the perfect material for a “looks-like” prototype—a part that lets you check the form and fit of a design before committing to a more expensive manufacturing process.

The Million-Dollar Question: What is the “+” in PLA+?

Here is the most important thing you need to understand: “PLA+” is not a standardized material. It is a marketing term.

Unlike ABS (Acrylonitrile Butadiene Styrene) or PETG (Polyethylene Terephthalate Glycol), which have defined chemical compositions, “PLA+” is simply a catch-all name that filament manufacturers use for their proprietary blends of PLA that have been modified for improved mechanical properties.

The secret is in the additives. The base is still PLA, but the manufacturer has blended it with impact modifiers and other polymers to change its behavior. Think of it like this: standard PLA is 100% PLA. PLA+ might be 90% PLA and 10% of something else. That “something else” is usually a type of polyurethane, most commonly TPU (Thermoplastic Polyurethane), the same stuff used to make flexible phone cases.

By adding a small amount of this rubbery polymer into the rigid PLA matrix, the manufacturers fundamentally change the way the material handles stress. Instead of the energy from an impact having nowhere to go but into a crack (brittle failure), the rubbery additives can absorb and dissipate that energy, allowing the part to flex and deform before it breaks. The material moves from brittle to ductile.

This is the magic of the “+”. It’s not necessarily stronger in the traditional sense (in fact, it’s often less stiff), but it is dramatically, phenomenally tougher.

A Tale of Two Jigs: My First “PLA+” Conversion

I remember the first time I truly understood the business value of PLA+. A medical device company came to us with a problem. They used dozens of 3D printed jigs on their assembly line to hold components in place. They were printing them in standard PLA because it was cheap and fast.

The problem was, their operators were human. They’d occasionally drop a jig, or knock it with a tool. Every time this happened, the PLA jig would shatter. They would lose 30 minutes of production time while someone ran to the print lab to grab a spare. It was costing them thousands of dollars a week in hidden downtime.

They asked me if we could machine the jigs from aluminum. We could, but it would cost them $300 per jig instead of the $5 in plastic they were currently spending.

I proposed a different solution. I took their exact same design and printed it on the same machine, but with a high-quality “tough PLA” (a brand of PLA+ I had been testing). The next day, I went to their facility. I handed the lead engineer the original PLA jig. I asked him to drop it on the concrete floor. It exploded into three pieces.

Then I handed him the new PLA+ jig. He dropped it. It bounced. He threw it against the wall. It left a mark on the wall. He took a hammer to it. The jig was dented and deformed, but it did not shatter. It had absorbed the impact.

The look on his face said it all. For a 20% increase in filament cost (from $5 to $6 per jig), we had eliminated thousands of dollars in weekly downtime. We didn’t make the jig “stronger” in the academic sense, but we made it tougher and more resilient for its real-world environment. That is the entire philosophy of PLA+.

We have established the core difference: standard PLA is stiff but brittle, while PLA+ is less stiff but dramatically tougher. Now, how does this play out in the numbers, and how does PLA+ stack up against the next level of engineering-grade filaments?

The Engineering Showdown: PLA vs. PLA+ vs. PETG

The story of the shattered jig illustrates the core principle, but in my factory, decisions aren’t made on stories alone. They’re made on data. To make a truly informed choice, we need to quantify the differences between these materials. And to make the comparison truly useful, we have to introduce the next logical step up the polymer ladder: PETG.

PETG (Polyethylene Terephthalate Glycol) is the same family of plastic used to make water bottles. It’s often seen as the bridge between the ease of PLA and the durability of more industrial materials like ABS. It occupies a critical middle ground, and understanding where it fits is key to making the right call.

Below is the comparison table I use with my own engineers. These are not absolute values—they vary slightly by manufacturer—but they represent the real-world performance you can expect. After the table, we will dissect exactly what these numbers mean for your parts.

Now, let’s break down what these rows actually mean.

Decoding the Data: Strength vs. Stiffness vs. Toughness

This is the most misunderstood concept in material science, and it’s the heart of the PLA vs. PLA+ debate.

• Stiffness (Flexural Modulus): This measures a material’s resistance to bending. A higher number means it’s stiffer. Notice that standard PLA is the stiffest material on the chart. This is why it feels so rigid and strong—until it snaps.
• Toughness (Impact Strength): This measures a material’s ability to absorb energy and deform without fracturing. This is the hammer test. Here, the story is completely reversed. PLA+ is 3-5 times tougher than standard PLA, and PETG is nearly twice as tough as PLA+.

Think of it this way:

• Standard PLA is like a glass rod. It’s very stiff and can hold a heavy weight without bending, but a sharp tap will shatter it.
• PLA+ is like a thick wooden dowel. It will bend noticeably under the same heavy weight, but you can hit it with a hammer and it will dent, not shatter.
• PETG is like a nylon rod. It’s even more flexible, and you’d have a very hard time breaking it with a hammer.

The takeaway: If your part needs to be absolutely rigid and won’t experience any sudden impacts, standard PLA is fine. If it’s a functional part that might be dropped, flexed, or snapped into place, PLA+ is the minimum requirement.

The Heat Problem: Glass Transition Temperature (Tg)

This is the second most important row. The Glass Transition Temperature (Tg) is the point where the polymer transitions from a hard, glassy state to a soft, rubbery one.

Notice something critical? PLA and PLA+ have the same poor temperature resistance. The additives that give PLA+ its toughness do nothing to improve its performance in a hot car. Both will warp into a useless puddle under the same conditions.

This is where PETG begins to show its value as a true engineering material. With a Tg of around 80°C, it provides an extra 20 degrees of thermal headroom. It’s the difference between a dashboard mount that survives a summer day and one that droops and drops your phone.

The Hidden Killer: Moisture (Hygroscopicity)

All 3D printing filaments are hygroscopic, meaning they absorb moisture from the air. But they are not created equal. When a filament absorbs moisture, the water molecules get trapped. During printing, this trapped water instantly flashes to steam in the hot end, causing pops, crackles, and bubbles. The result is a weak, stringy, ugly print with terrible layer adhesion.

PLA and PLA+ are relatively resistant to moisture. You can leave a spool out for a few weeks in a normal environment and it will likely still print fine.

PETG, however, is a moisture sponge. A spool of PETG left out in a humid environment for just a few days can be ruined. At RM, we store all our PETG spools in sealed containers with desiccant packs, and for critical jobs, we actively dry the filament in a dedicated oven for 4-6 hours before printing. This is a step most hobbyists don’t take, and it’s the number one reason they struggle with PETG.

The Printing Experience: Ease of Use & Practicality

There’s a reason PLA is king: it’s incredibly forgiving. It sticks to almost any build surface, doesn’t require an enclosure, and produces beautiful results with minimal tuning. It’s the “it just works” material.

PLA+ is nearly as easy, but it likes to be printed a bit hotter (usually 10-15°C higher) to ensure the additives are fully molten and the layers bond properly. It also benefits from good part cooling to maintain sharp details.

PETG is where the learning curve steepens. It is notoriously prone to “stringing” or “oozing,” leaving fine, spiderweb-like hairs all over the print. This can be managed with careful tuning of retraction settings, but it requires more effort. It also needs a hotter nozzle (230-250°C) and a heated bed (70-85°C) is mandatory for good adhesion.

A Quick Case Study: The Drone Landing Gear

A client, an agricultural drone startup, was prototyping landing gear. They started with standard PLA. The parts looked perfect, but on the first hard landing, the gear shattered, risking the expensive camera payload.

They switched to PLA+. This was a huge improvement. On hard landings, the gear would now flex and absorb the impact. It would deform and bend out of shape, but it wouldn’t shatter. This was acceptable for prototyping, but they found that after a few hard landings, the bent gear had to be replaced.

Finally, we printed the part in PETG. It was the perfect balance. It was flexible enough to absorb the hard landings without breaking, but it was also stiff enough to spring back to its original shape unless the impact was truly catastrophic. Furthermore, the drone often sat on hot asphalt tarmacs, and the PETG’s higher Tg prevented the gear from slowly deforming in the sun. For a slightly higher material cost and a bit more print tuning time, they got a functional part they could actually use in the field.

We’ve established the material properties and their practical implications. The choice seems clear: PLA for looks, PLA+ for toughness, and PETG for durability. But this is only half the equation. A great material cannot save a bad design. How do you design your part to leverage the strengths of these materials and avoid their weaknesses?

Design for Additive Manufacturing (DfAM): Turning Material into Money

We’ve established the material properties and their practical implications. The choice seems clear: PLA for looks, PLA+ for toughness, and PETG for durability. But this is only half the equation. At my factory, I’ve seen million-dollar materials produce ten-dollar results because of poor design. Conversely, I’ve seen engineers work miracles with cheap filament because they understood one critical truth: A great material cannot save a bad design.

The process of designing a part specifically for the 3D printing process is called Design for Additive Manufacturing, or DfAM. It’s the difference between fighting the machine and working with it. Below are the five most important DfAM rules we live by at RM. Ignoring them is the fastest way to turn a spool of high-performance filament into a pile of expensive scrap.

Rule 1: Orient for Strength, Not for Speed

This is the non-negotiable, cardinal rule of Fused Deposition Modeling (FDM). Every part you print has an invisible wood grain, formed by the layer lines. The bond between the layers is always significantly weaker than the strength of a single, continuous strand of extruded plastic. This property is called anisotropy, and if you ignore it, your parts will fail.

Imagine a simple bracket designed to hold a shelf.

• Wrong Orientation: If you print the bracket standing up on its end, the layer lines will be parallel to the shelf. The force pulling down on the shelf will be trying to peel the layers apart—the weakest possible direction. It will snap.
• Right Orientation: If you print the bracket lying flat on its back, the layer lines will be perpendicular to the force. The force is now pulling against the long, continuous strands of plastic. The part will be at its maximum possible strength, often 5-10 times stronger than the incorrectly oriented version.

A Case from My Factory: We were printing a series of C-clamps for a new engineer’s assembly station using PLA+. The design was fine, but the first batch kept snapping at the top of the “C” as soon as he tried to tighten them. I walked over, looked at the broken parts, and could see the clean, sheer layer lines. He had printed them standing up to fit more on the build plate at once. We printed a single clamp, oriented on its side, and it worked perfectly. It took four times as long to print one, but the first batch was 100% scrap. His attempt to save a few hours of print time cost us a day of work and a kilogram of filament.

Rule 2: Master the 45-Degree Rule for Overhangs

An FDM printer builds a part layer by layer. This means it can’t print in mid-air. Any feature that extends out over empty space is called an overhang. Most modern printers can handle overhangs up to about 45 degrees without any issue, as each new layer is sufficiently supported by the one below it.

As you approach 60 degrees, you’ll see drooping and poor surface quality. At 90 degrees (a flat, horizontal overhang), the printer is just squirting molten plastic into the air, and you’ll get a catastrophic failure.

The solution is either to add support material (which adds time, cost, and post-processing) or, preferably, to design the feature out.

• Instead of a flat 90-degree overhang, can you use a 45-degree chamfer?
• Instead of a round-bottomed hole on the side of a part, can you change it to a teardrop shape?

This simple consideration separates an amateur designer from a professional. The pro designs a part that prints itself without needing a forest of wasteful support material.

Rule 3: Use Fillets and Chamfers to Manage Stress

This rule is especially critical when working with brittle materials like standard PLA. Sharp internal corners are “stress concentrators.” When a force is applied to the part, all the stress flows to that one tiny point, making it incredibly easy to start a crack.

By adding a fillet (a rounded internal corner), you give the stress a smooth path to flow along, distributing it over a much larger area and dramatically increasing the part’s strength. This is one of the easiest and most effective ways to make your parts more robust. For PLA+, which is tougher but still benefits from good design, fillets can be the difference between a part that flexes and one that eventually yields to fatigue.

Rule 4: Design Holes Slightly Oversized

This is an insider’s tip that will save you hours of frustration. A 10mm hole in your CAD model will never come out as a 10mm hole on an FDM printer. It will always be slightly smaller, typically by 0.2mm to 0.5mm, depending on the printer, material, and slicer settings.

This happens for two reasons: thermal shrinkage of the plastic as it cools, and the “squish” of the first few layers. If you are designing a multi-part assembly where pins need to fit into holes, you must account for this. We have a standard practice at RM: for a clearance fit, we model the hole 0.3mm larger than the pin. For a tight press-fit, we model it exactly to size or just 0.1mm oversized, knowing it will come out slightly smaller and require force to insert the pin. Not accounting for this is the number one reason client-designed assemblies don’t fit together on the first try.

Rule 5: Wall Thickness is More Important Than Infill Percentage

Beginners obsess over infill percentage, thinking that a 100% infill part is the strongest. It’s almost never true. The strength of an FDM part comes primarily from its outer walls, or “perimeters.”

Think of it like building a house. The exterior walls provide the vast majority of the structural integrity, not the drywall inside. Doubling the number of perimeters (e.g., going from 2 walls to 4 walls) has a much greater impact on strength than increasing infill from 20% to 50%. It also often uses less material and takes less time to print. For 95% of the functional parts we print at RM, we use 4-6 walls with a modest 25-40% infill. A 100% infill is a waste of material and can even weaken the part by introducing massive internal stresses as the plastic cools.

Final Verdict: Choosing the Right Tool for the Job

So, which is better, PLA or PLA+? After all this, the answer is simple: It depends entirely on the job.

• Choose Standard PLA when your primary concerns are aesthetics, fine detail, and stiffness, and the part will not be subjected to impact, flexion, or temperatures above 50°C. It is the perfect material for visual prototypes, architectural models, and display pieces.
• Choose PLA+ (Tough PLA) when you need a functional part that can withstand impacts, drops, or bending. It is the ideal material for works-like prototypes, jigs, fixtures, and parts with snap-fit features. It is the go-to, general-purpose engineering filament.
• Choose PETG when you need the toughness of PLA+ combined with better temperature resistance and UV stability. It is the right choice for parts used outdoors, in hot environments, or for mechanical components that require a bit more durability and chemical resistance.

The material is only the first choice. True success comes from understanding the material’s properties and designing the part to leverage them. By following good DfAM principles, you move from just printing objects to engineering solutions.

Frequently Asked Questions (FAQ)

So, which is actually “stronger,” PLA or PLA+?

This is the trick question. Standard PLA is stiffer (resists bending better) but PLA+ is tougher (resists impact better). For most functional applications, toughness is the more important type of strength, making PLA+ the “stronger” choice for real-world use.

Can I use my standard PLA print settings for PLA+?

Almost. You will get the best results, especially with layer adhesion, by increasing your nozzle temperature by 10-15°C compared to standard PLA. Everything else (bed temperature, speeds, retraction) can usually remain the same.

When should I absolutely choose PETG over PLA+?

There are two main triggers. First, if the part will be used in an environment that could exceed 60°C (140°F), like inside a car on a sunny day. Second, if the part will have prolonged exposure to direct sunlight. The UV resistance of PETG is far superior to any type of PLA.

What is the single biggest cause of failed prints with these materials?

For PETG, the number one cause is wet filament. For PLA and PLA+, the most common failures I see stem from incorrect part orientation (violating DfAM Rule #1) or a poorly leveled bed causing first-layer adhesion problems.

Is PLA+ really worth the extra 20% cost?

If you are printing a non-functional display piece, no. If you are printing a functional part, absolutely. The cost of a single broken part—in reprint time, wasted material, and potential damage to whatever it was attached to—almost always exceeds the small premium you pay for the entire spool of PLA+. It’s an investment in reliability.

References for Further Reading

• MatterHackers – Filament Comparison Guide: https://www.matterhackers.com/filament-comparison-guide (An excellent real-world database of filament properties and printing characteristics from a major supplier.)
• PrusaPrinters – The Basics of 3D Printing with PLA: https://help.prusa3d.com/materials-pla (A comprehensive guide from a leading printer manufacturer covering the practical aspects of printing with PLA.)
• Ultimaker – Design for Additive Manufacturing: https://ultimaker.com/learn/design-for-additive-manufacturing-dfam/ (A series of expert articles covering the core principles of DfAM, including overhangs, wall thickness, and orientation.)

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