A Maker Guide to 3D Printing with Flexible Filaments

Flexible 3D printing filaments are often avoided due to a reputation for jammed extruders, stringing, and failed prints. However, achieving successful results with bendable, shock-absorbing parts comes down to understanding material hardness, selecting the right grade for the project, and using appropriate hardware configurations.

Understanding the Shore Hardness Scale

Flexible materials are categorised by their Shore Hardness, which measures resistance to indentation. The most common scales encountered in desktop manufacturing include Shore 00 for extremely soft gels, Shore A for rubber-like elastomers, and Shore D for rigid plastics.

• Shore 00: Used for very soft rubbers and light foams. Filaments are rarely measured on this scale because the material is too soft to push through an extruder gear without buckling.
• Shore A: Measures softer elastomers ranging from elastic rubber bands to firm shoe soles. Almost all flexible 3D printing filaments use the Shore A scale.
• Shore D: Used for hard rubbers, semi-rigid plastics, and rigid thermoplastics.

When shopping for flexible filaments, makers typically look at the higher end of the Shore A scale. A 90A TPU offers high dynamic compression and rebound, feeling similar to dense running shoe foam. A 95A TPU, often formulated as high flow (HF), is firmer like a skateboard wheel, offering enough stiffness to feed easily at higher speeds while still absorbing impact.

Core Flexible Filament Types

Flexible plastics span several categories:

• TPE: Thermoplastic Elastomer is the umbrella term for the entire family of rubber-like 3D printing plastics. Older or unbranded TPE blends are often ultra-soft.
• TPU: Thermoplastic Polyurethane is a specific child within the TPE family and acts as the modern industry standard. Variants like TPU 90A suit wearables and padding, while TPU 95A HF provides a high-flow workhorse for phone cases and gaskets.
• TPC: Thermoplastic Copolyester is an engineering-grade flexible filament providing high temperature and chemical resistance, suited for automotive and mechanical applications.
• Soft PLA: Standard PLA treated with chemical plasticizers to create a bendable, non-stretchy material suitable for decorative costume pieces or hinges.

Hardware and Slicer Settings for Success

Printing flexible materials requires specific mechanical setups and slicing parameters. Pushing soft TPU through a long Bowden tube often results in buckling and jams. A direct-drive extruder, where the drive gears sit directly above the hotend, is strongly recommended to control the filament path.

Filament moisture management is another critical factor. TPU is hygroscopic and absorbs ambient humidity, causing moisture to boil inside the nozzle, which leads to popping, stringing, and weak prints. Drying spools thoroughly at recommended temperatures before printing is essential.

In the slicer, makers should use manual loading procedures rather than automated load functions to avoid gear knotting. Retractions should be kept short and slow on direct-drive setups to prevent the elastic material from stretching and causing under-extrusion. When printing functional parts like shoe soles with ultra-soft TPU 90A, using a gyroid infill density of 15% to 20% helps achieve proper cushioning.

What This Means For South African Makers

Local hobbyists and small businesses often contend with high ambient humidity during wet seasons, which makes moisture control vital for materials like TPU. Ensuring that flexible filaments are kept in dry boxes or active filament dryers before and during long print jobs eliminates porosity and stringing issues. Choosing the right Shore hardness also helps local designers match functional requirements, using 95A for durable protective enclosures and 90A for custom vibration dampers or ergonomic grips.

DC3D’s Take

Tackling flexible filaments can test any maker’s patience, but understanding the nuances of Shore hardness and shifting away from Bowden setups solves most common extrusion headaches. Direct-drive extruders have made printing TPU far more accessible on modern desktop machines. Taking the time to properly dry hygroscopic materials and tune retraction settings transforms flexible printing from an exercise in frustration into a reliable workflow for functional parts.