What’s Soft PLA Filament: A Comparative Analysis with TPU

Flexible Filament 101

3D printing provides unparalleled flexibility when it comes to the construction of custom-made models. Whether you’re looking for a special material, design accuracy or repeatability, the filament used for 3D printing is sure to fulfil your requirements.  

The thermoplastic elastomer, also known as a polymer of hard plastic and rubber, is used to create the majority of flexible filaments. Their incredible flexibility comes not only from their unique combination of hard plastic and rubber but also from the unique ratio in which these elements are mixed, providing users with a wide range of possibilities. 

With thermoplastic elastomers, you can print items as soft and pliable as a rubber band – objects that are able to flex and bend without any worry that they might break – all the way up to strong tires used on automobiles that remain firm while being pressured and flexed. 

There are several different kinds of flexible filament available, each with unique qualities and advantages:

• TPE: Thermoplastic elastomer, or TPE for short, is a versatile and broadly applicable material used in 3D printing. It combines the attributes of thermoplastics and elastomers to create a flexible filament that is an ideal choice for applications in which the object needs to be both durable and bouncy.
• TPU: Also known as thermoplastic polyutherane, is slightly more rigid than its counterpart but can easily be worked with typical extruders to make higher-quality prints.  
• TPC: The latest in 3D printing filament technology. This innovative co-polyester filament is partially composed of bio-oils, making it not only eco-friendly but incredibly durable as well. Despite its strength, however, it can still buckle very easily if it’s not printed slowly enough – a fact that can cause significant warping issues with prints.
• PCTPE: It is a wonderful tool that allows Creators the ability to combine the strength of nylon and the flexibility of TPE. This robust filament allows users to take their creations to the next level. Not only is it flexible, but also heat resistant, with a softer feel than other materials.
• Soft PLA: This biopolymer has flexibility and strength that enables the creation of strong, long-lasting items that won’t snap or break. Additionally, this variant of PLA can be used to easily produce intricate shapes and designs which couldn’t otherwise be made with regular plastic filaments. 

Printing Tips

Flexible filaments offer many advantages for production and prototyping, but their increased difficulty to work with due to their pliable nature must be taken into account. When compared to stiffer base materials from which filament is usually made, flexible filaments dampen impacts and vibrations more effectively, have a longer shelf life, and are far more resistant to wear and tear. 

If you are looking for the highest quality flexible prints, using a direct drive extruder is one of the best methods. It significantly increases the chances of getting a perfect print as it shortens the distance between the drive gear and the melts zone as much as possible. This allows your flexible filament to move more freely through the printer, decreasing the opportunity for bunching and yielding better results in the end. 

Understanding its Nature

As previously mentioned Soft PLA is a unique, sustainable 3D printing material that takes advantage of nature’s resources by using natural materials like cornstarch, tapioca roots, and sugarcane to create a uniquely flexible filament. As with regular PLA for 3D printing, soft PLA starts out as a liquid that’s melted down and formed into pellets. From there the pellets are processed and shaped into long segments of filament that can be wound up onto spools for easy, convenient 3D printing.  

Soft PLA is a special variant of the standard printer plastic that has chemicals added to it for enhanced performance and usability. Unlike regular PLA, which is quite brittle and susceptible to cracking under pressure, soft PLA can be manipulated with pressure applied and still spring back to its original shape after the pressure is removed. 

The additional chemicals also give soft PLA characteristics of rubber, giving it the ability to absorb vibrations and impacts in addition to maintaining its shape after exterior pressures. This makes it particularly useful for items like toy car tires where a good grip on the track or road surface is required without sacrificing strength or flexibility in the material.

Following a breakdown of the advantages and disadvantages of soft PLA, we’ll compare it to TPU filament.

Advantages

Soft PLA’s advantages over regular PLA include:

• Ergonomics: This lightweight and flexible filament material can be tailored to cover the full spectrum of variable softness, making it optimal for ergonomically designed objects. From products like pen grips and shoe sole inserts to polishing compounds and wallpapers, the benefits of soft PLA abound.
• Low carbon footprint: It offers a flexible product that still maintains a lower carbon footprint and biodegradable characteristics like regular PLA. This is due to the fact that while its manufacturing process uses more chemicals than traditional filaments, it remains a better option than other types of flexible filaments. 
• Durability and flexibility: While PLA has many beneficial properties, it results in very brittle objects which limits its application. However, soft PLA provides the best of both worlds by having the same great benefits as traditional PLA such as high resolution and durability without sacrificing flexibility. This opens up a world of possibilities for 3D printing enthusiasts – from small items like phone cases to large ones like car tires, the unique traits of soft PLA make it well-suited for virtually any project that needs strength as well as flexibility.

• Vibration dampening: The combination of flexibility, strength and durability makes it an incredibly useful material for dampening components, protecting surrounding parts from vibration and motion. 

Disadvantages

The biggest challenge when using soft PLA filament is learning what does and doesn’t work to make it do what you want. It’s got a few downsides that also stem directly from its added flexibility properties:

Working with soft PLA filament presents unique challenges compared to the standard filament. It can be tricky to learn what works and what does not with this specific material, but it also opens up a world of possibilities for custom 3D printing designs. Despite its many advantages, such as its flexibility, there are a few drawbacks to consider when using this kind of filament.

• Printing difficulty:  Soft PLA is generally considered to be a rather difficult material to use for 3D printing, as compared to its more rigid cousins. This is due to its inherent lack of tension and reduced adherence which causes it to easily clog, bubble, and bunch up during the drawing process. In order to avoid executing prints that are sub-par quality and riddled with defects, you’ll need extra attention and precision when working with this kind of filament. Fortunately, some changes in your 3D printing settings can help make soft PLA much easier to manage. Slowing down the printing speed will apply extra force on both the feeder itself, making sure that strands remain even throughout the print job, as well as giving it more direction once on the bed. 
• Special hardware: For those looking to use softer PLA formats in 3D printing, there is no shortage of helpful tools. A direct drive extruder is a great way to ensure that the filament takes minimal and smooth turns on its journey from the feeding entrance to the print bed, ensuring that soft PLA won’t catch unnecessarily. Additionally, there are special adhesion liquids designed specifically for softer PLA which works wonders by keeping the material firmly in place while printing.  
• Poor support material: Despite its flexibility, soft PLA isn’t the best filament for providing structural support in 3D objects. Its malleable nature means it’s not suitable for designs with open gaps or sharp overhangs, which require a more rigid material to retain integrity — though it can be great for printing objects with smooth surfaces. 

Contrasting with TPU

Soft PLA and TPU have a lot in common, but there are a few notable differences:

• Stiffness: TPU and soft PLA filaments have similar rigidity levels but small differences can make big impacts when it comes to 3D printing materials. According to the Shore scale of rigidity, while TPU measures 94A–95A, soft PLA filament is slightly behind at an average of 92A. Although this difference may seem insignificant, one might find this a game-changer during the 3D printing and post-printing processes. With its high degree of flexibility and strength, TPU is by far easier to work with compared to other more rigid materials like ABS and nylon.
• Food safety: Soft PLA is a unique 3D printing material specifically formulated with food-safe components, which makes it ideal to use as food containers or utensils that may be frequently handled directly by users. From cookie cutters to teething toys for babies, any object that is meant to touch or enter the mouth can safely be printed using soft PLA. Of course, eating the soft PLA itself should not be done; nonetheless, by taking the appropriate post-processing measures once the object has been printed, one can ensure that its contact with edibles is safe and hygienic. On the contrary, TPU materials should generally be avoided for contact with food due to their chemical composition.
• Abrasion reisistance: TPU has notably increased abrasion resistance, making it better suited for 3D printing projects that require projects to endure regular contact or movement. For example, TPU-printed machine parts last significantly longer than PLA-printed parts due to their extra rigidity; in most industrial settings, this handy feature allows for fewer replacements and costs over time. 
• Flexibility: Soft PLA filaments due to their greater flexibility are perfect for anyone wanting to print a garment or accessory, like a belt or headband. Its softness allows it to deform easily with natural body movements, so none of the printed pieces will break when flexed.

Gunaseelan Murugesan

Author | Website

Experienced Project Engineer with a demonstrated history of working in the field of Product Design & Development industry in Mechanical Engineering. Skilled in 3D Printing and Re engineering Technologies with CATIA V5 , Materials Science, Finite Element Analysis (FEA), Mimics, ANSYS Workbench and Casting Simulation software. Strong engineering professional with a Master’s Degree focused in Industrial Metallurgy from PSG College of Technology, Coimbatore.