Common PTFE Liner Defects during Catheter Manufacturing

The PTFE is one of the slipperiest solid materials known to man. As a result it is typically the best choice of material for catheter liners due to its incredibly low coefficient of friction. PTFE liners form the innermost surface of many catheter shafts. Its task is to ensure a safe, lubricious inner lumen, allowing smooth passage of devices like guidewires, fluids, and instruments.

Although PTFE as a material is a great fit for liners, the performance of the catheter depends ultimately on the quality of the liner. Even minor defects in PTFE liner manufacturing or adhesion can compromise the entire catheter. Issues such as wall thickness variation, pinholes, surface contamination, and etching degradation often go undetected until reflow or final inspection. This, of course, is when the cost of failure are highest. 

Detecting liner defects early is therefore much more cost-effective than reworking finished assemblies.

Defect-free PTFE liners are essential for high-performance catheters and advanced delivery systems manufacturing. So understanding common issues is essential so they can be prevented. 

In this article we will use Hydromer®, Inc.’s 40+ years of materials expertise to examine the most common PTFE liner defects, the manufacturing pitfalls that cause them, and the inspection practices that catch them before they reach the production floor.

Role of PTFE Liners in Catheter Performance

A PTFE liner sits between the lumen and the reinforcement structure. Their main role is to create a smooth inner pathway for everything that passes through the catheter. Guidewires, stylets, embolic coils, and fluids all travel across this surface during operational procedures.

The main job of a PTFE liner is to reduce friction inside the lumen. PTFE has a coefficient of friction(CoF) of approximately 0.04, which is among the lowest of any solid material. This creates a high level of lumen lubricity. And this allows physicians to advance and retract guidewires and instruments smoothly, without the drag that raises procedure time and clinical risk.

Beyond reducing friction, a PTFE liner serves several critical functions in the finished catheter:

• Structural Integrity: The PTFE liner keeps the lumen round and open when the catheter bends through tight vasculature. It resists collapse and kinking, helping instruments and fluids pass freely at every point along the shaft.
• Chemical Inertness: PTFE is generally considered non-reactive with contrast media, drugs, or body fluids. The liner acts as an inert barrier between these substances and the outer layers of the catheter.
• Biocompatibility: PTFE is generally considered to be non-toxic and non-carcinogenic under normal operating conditions. This makes it a suitable material for the surface that contacts fluids entering the patient.

Common PTFE Liner Defects in Catheter Manufacturing

Defect Category	Common Root Cause	Best Detection Method
Dimensional (Wall Variation/Ovality)	Processing stress, soft material tolerances	Laser Measurement Systems
Surface Flaws (Pinholes/Scratches)	Tooling contact, resin impurities	Optical Microscopy / Pressure Leak Testing
Adhesion Failures (Delamination)	Under-etching, over-etching, or aged PTFE	Peel Testing
Processing-Induced (Print-Through)	Excessive heat/pressure during reflow	Friction Testing / Sectioning

PTFE liner defects can arise at any stage of catheter manufacturing. Some originate during liner production, while others occur during etching, braiding, reflow, handling, or storage. Each stage presents unique risks that must be understood.

The real challenge is that many liner defects are not visible to the naked eye. A pinhole, a micro-void, or an under-etched surface looks identical to a good liner during a quick visual check. These defects often stay hidden until reflow or final testing, when the cost of scrap is at its highest.

Below, we have grouped the most common PTFE liner defects into six categories:

1. Dimensional Defects in PTFE Liner Production

Dimensional defects are simply the deviations in the physical geometry of the liner that happen during fluoropolymer liner manufacturing. These defects are among the most common PTFE liner problems. This is due to the fact that PTFE is a soft material and difficult to process within tight tolerances. Even small dimensional errors can affect how the liner performs inside the finished catheter.

Key dimensional defects to be aware of and monitor include:

• Wall Thickness Variation: This defect occurs when the liner wall is thicker in some sections and thinner in others along its length. Thin spots weaken the liner and raise the risk of burst or perforation. Thick spots reduce the usable lumen space.
• Liner Eccentricity: This happens when the inner and outer diameters are not centered on the same axis. It creates one thin side and one thick side around the circumference. The thin side becomes a weak point during reflow and during clinical use.
• Ovality: Ovality is the deviation of the liner cross-section from a perfect circle. An oval lumen creates uneven clearance for guidewires and instruments, causing inconsistent friction at different points.
• Inner Diameter (ID) Variation: This defect refers to changes in the lumen diameter along the liner length. A tight section can grip the guidewire and cause resistance, while a loose section reduces support and control. Such a variation is particularly problematic in the case of long catheters.
• Liner Collapse: It occurs when a section of the liner flattens or caves inward, leading to partial or full blockage of the lumen. Collapse is often triggered during reflow or bending operations when the liner wall is too thin or unsupported.
• Wrinkles and Buckling: These are folds or ripples that form on the liner surface when it is compressed along its length. Wrinkles create high spots inside the lumen that catch guidewires and increase friction. They commonly appear during assembly when the liner is pushed instead of pulled over the mandrel.

2. Surface Flaws

Surface defects impact the inner or outer liner surfaces rather than the overall geometry. Most are microscopic and more difficult to detect than dimensional defects.

Such defects rarely announce themselves during assembly. A PTFE liner with pinholes or microcracks will often build into a catheter without any visible sign.

• Surface Scratches: These are linear marks on the liner surface caused by contact with rough tooling, mandrels, or handling equipment. Scratches on the inner surface increase friction and can catch guidewire tips during a procedure. Deep scratches also act as stress points where cracks can start.
• Embedded Foreign Particles: These are particles trapped inside the liner wall during extrusion or casting. Metal fragments, dust, or degraded polymer can embed into the soft PTFE. Such embedded particles create weak spots in the wall and can protrude into the lumen as raised bumps.
• Surface Contamination: This refers to oils, dust, mould release agents, or other residues sitting on the liner surface. Contamination on the outer surface interferes with etching and bonding, while contamination inside the lumen can transfer to fluids passing through.
• Poor Internal Surface Finish: A rough or textured lumen surface that raises friction across the entire liner length. Unlike a scratch, which is localized, a poor surface finish is a distributed defect that comes from the manufacturing process itself. It reduces the low-friction benefit that is the main reason for using PTFE in catheter manufacturing.
• Pinholes: Tiny holes that pass partially or fully through the liner wall. Pinholes allow fluids to leak into the catheter structure and compromise the barrier function of the liner. They are especially dangerous in thin-walled liners, where a single pinhole can grow into a full perforation under pressure.
• Microcracks: These are hairline cracks in the liner wall that are invisible without magnification. Microcracks are formed due to processing stress, bending, or material fatigue. Under repeated flexing during a procedure, they can propagate and lead to liner failure inside the patient.

3. PTFE Liner Etching and Adhesion Failures

PTFE is inherently non-stick, making it difficult to bond to other catheter materials, such as the outer jacket.

Therefore, the outer surface of PTFE liners must be etched to allow catheter jacket materials (PEBAX, Nylon, TPU, etc.) to adhere during catheter shaft reflow. Most adhesion issues originate from the etching process or bond interface and are costly to detect, as they often appear only after catheter assembly.

• Under-Etched PTFE: Occurs when the etching treatment does not sufficiently activate the outer surface. The jacket material appears bonded after reflow, but the bond strength is low.
• Over-Etched PTFE: Happens when the etching treatment is too aggressive and degrades the PTFE surface. The treated layer becomes weak and chalky, so the jacket bonds to a damaged surface rather than a strong one.
• Uneven Etching: Refers to inconsistent surface treatment along the liner length or around its circumference. Some areas bond well while others bond poorly, creating unpredictable weak zones.
• Aging of Etched PTFE: Etched surfaces lose their bonding ability over time, especially when exposed to light, heat, or humidity. A liner that was properly etched can behave like an under-etched liner after months of poor storage. This is why etched liners carry a shelf life and defined storage requirements.
• Delamination Between PTFE and Jacket: The separation of the liner from the outer jacket after the catheter is built. Delamination can start from any of the etching defects above or from insufficient heat and pressure during reflow.
• Air Voids at the Bond Interface: These are trapped air pockets between the liner and the jacket that form during reflow. Voids reduce the bonded contact area and act as starting points for delamination.

4. Material Defects

Material defects originate in the PTFE resin itself, before the liner is even formed. They are the hardest category for catheter manufacturers to control because the defect enters the supply chain at the raw material stage.

In most cases, a sudden rise in things like pinholes or wall thickness variation may point to the resin batch rather than the extrusion line. As such, keeping records that link each liner lot to its resin batch helps engineers trace the true root cause quickly.

• Resin Contamination: It occurs when foreign substances mix into the PTFE resin before or during processing. Contaminants such as metal particles, degraded polymer, or other resin grades create impurities throughout the liner wall.
• Material Voids: These are microscopic empty pockets inside the liner wall that form when the resin does not consolidate fully during processing. Voids weaken the wall and reduce its burst strength.
• Low-Quality PTFE Resin: Low-grade resins may contain higher levels of impurities, inconsistent particle sizes, or reprocessed material. Liners made from such resin show unpredictable mechanical properties and higher defect rates.

5. Processing-Induced Defects

These defects occur during catheter assembly, not during Fluoropolymer liner manufacturing. Liners may arrive in good condition but become damaged during braiding, reflow, or other downstream operations. Because these defects are within the manufacturer’s control, they are preventable but costly if overlooked/unprevented.

• Heat Reflow Damage: It occurs when the reflow temperature or dwell time exceeds what the liner can tolerate. Excessive heat can reduce wall thickness, distort the lumen, or degrade the PTFE surface. The damage is often hidden under the jacket and only appears during sectioning or leak testing.
• Excessive Heat Shrink Pressure: Happens when the heat shrink tubing used during reflow compresses the liner too aggressively. The pressure can push the liner inward, reduce the lumen diameter, or create flat spots.
• Incomplete Polymer Flow Through Braid or Coil: Occurs when the jacket material does not fully penetrate the reinforcement layer during reflow. The result is air gaps between the liner, the braid, and the jacket. These gaps weaken the shaft structure and act as starting points for delamination.
• Reinforcement Print-Through: It happens when the braid or coil pattern presses into the soft liner during reflow and leaves an impression on the lumen surface. The textured pattern raises friction inside the lumen and can catch guidewire tips. Print-through typically results from too much heat, too much pressure, or a liner wall that is too thin for the reinforcement design.
• Thermal Expansion Mismatch: Refers to the stress created when the liner and the jacket expand and contract at different rates during heating and cooling. The mismatch can leave residual stress in the shaft, which later shows up as wrinkling, delamination, or dimensional drift.
• Liner Stretching During Assembly: It occurs when the liner is pulled with too much tension while being loaded onto a mandrel or during reflow setup. Stretching thins the wall, reduces the outer diameter, and can leave residual stress in the material.

6. Handling and Storage Issues

Last but not least, handling and storage defects also need to be looked out for. These are the most avoidable categories on this list, but can still happen. The liner leaves manufacturing in good condition and gets damaged before it ever reaches the assembly line.

Because PTFE is soft and has low resilience, it typically retains physical damage rather than recovering from it.

• Kinks from Improper Handling: These are sharp bends that crease the liner wall during unpacking, transfer, or loading. A kink creates a permanent weak point where the wall is stretched on one side and compressed on the other. Even after straightening, the kinked section remains prone to collapse and cracking.
• Permanent Deformation During Storage: It occurs when liners are stored coiled too tightly, hung under tension, or stacked under weight. PTFE slowly takes the shape it is held in. Such behavior is commonly known as cold flow. A liner stored incorrectly for months can develop ovality, curvature, or flat spots that cannot be reversed.
• Damage During Packaging and Transportation: It refers to scratches, dents, and crushed sections caused by inadequate packaging or rough transit. Liners shipped without protective spools or rigid containers can rub against each other or the packaging itself.
• Incorrect Mandrel Fit: It happens when the liner is loaded onto a mandrel that is oversized or undersized for its inner diameter. An oversized mandrel stretches the liner and thins the wall, while an undersized mandrel lets the liner wrinkle and shift during reflow.

How PTFE Liner Defects Are Detected

When it comes to medical device manufacturing, defect detection must happen at the right point in the process to prevent regulatory complications and ensure patient safety.

In the case of catheters, some detection methods work best at incoming inspection, while others only make sense after reflow, when the bond and the finished lumen can be evaluated. The goal is to catch each defect at the earliest stage where it becomes measurable.

At Hydromer®, Inc., we use the following detection methods to ensure precise catheter manufacturing:

1. Visual Inspection

It is the first and simplest check. Trained inspectors look for kinks, scratches, discoloration, contamination, and visible deformation under good lighting or low magnification.

Visual inspection catches gross defects quickly, though it cannot detect microscopic flaws.

2. Laser Measurement Systems

These are non-contact systems that measure outer diameter, wall thickness, and ovality continuously along the liner length. Laser micrometers detect dimensional drift, eccentricity, and thin spots that hand gauges miss.

This is the most reliable way to verify that a liner meets its dimensional specification from end to end.

3. Optical Microscopy

Optical Microscopy is used to examine the liner surface and cross-sections at higher magnification. Microscopy reveals scratches, embedded particles, pinholes, and microcracks that are invisible to the naked eye. Cross-sectional microscopy also confirms wall uniformity and detects voids inside the material.

4. Peel Testing

This testing measures how strongly the jacket material adheres to the etched liner surface after reflow. A controlled peel pulls the layers apart while recording the force required. Peel testing is the standard method for catching under-etched, over-etched, and aged liners before they reach production volume.

5. Friction Testing

It verifies that the lumen surface delivers the low-friction performance expected from PTFE.

A test wire or any suitable instrument is passed through the liner while the pull force is recorded. Rising friction values point to surface roughness, print-through, wrinkles, or contamination inside the lumen.

6. Pressure Leak Testing

Such testing checks the liner wall for pinholes and perforations by applying air or fluid pressure and monitoring for leakage. Leak testing is critical for thin-walled liners where a single pinhole compromises the barrier function. It is often performed both on incoming liners and on finished catheter assemblies.

Best Practices to Prevent PTFE Liner Defects

While detection identifies existing defects, prevention techniques are designed to stop defects from occurring.

Each liner rejected at final inspection incurs the full cost of material, labor, and processing time. A prevention-focused quality strategy is therefore more cost-effective than relying heavily on inspection.

Prevention is most effective when it spans the entire liner journey, from the supplier’s production line to the reflow station. The following practices are most effective at minimizing defects:

1. Supplier Qualification

It is the single most effective prevention step because most material and dimensional defects enter through the supply chain.

Qualify liner suppliers based on process capability, resin traceability, certifications, and defect history, not price alone. Suppliers should provide lot-level documentation linking each liner batch to its resin batch to enable effective root cause analysis.

Suppliers such as Hydromer®, which manufactures liners under ISO 13485:2016-certified processes, control dimensional and material defects at the source. Re-qualify suppliers periodically, as equipment, resins, and personnel may change over time.

2. Incoming Inspection

Incoming inspection is the first and most effective opportunity to reject defective liners before additional value is added. Establish a written inspection plan that includes dimensional checks, visual examination, and documentation review for each lot. Verify the actual measured ID against mandrel sizes, as small deviations can cause stretching or wrinkling.

Photograph and record any damage found at receiving, which protects both you and the supplier during defect investigations. A liner that fails incoming inspection costs only the material; the same liner failing after reflow costs the entire assembly.

3. Proper Storage

Proper storage prevents gradual, often unnoticed damage to PTFE during inventory. Store liners on appropriately sized spools or in rigid containers, avoiding tight coils or tension, as PTFE will conform to the shape in which it is stored.

Store etched liners away from light, heat, and humidity, and strictly enforce shelf life, as aged etching loses effectiveness. Use first-in, first-out rotation to minimize storage time. Maintain a clean, controlled storage area to prevent dust and contamination that can affect bonding.

4. Optimized Etching

Optimized etching ensures reliable bonding of the outer surface without damaging the underlying PTFE. Whether performed in-house or by the supplier, the process window must be defined, documented, and verified through regular peel testing.

Both under-etching and over-etching result in weak bonds; the objective is to achieve a validated, optimal process window. Confirm etch uniformity along the length and circumference, as uneven etching creates weak zones. Record the etch date for each lot to enforce shelf-life limits.

5. Controlled Reflow Process

A controlled reflow process protects the liner during the most thermally aggressive step of catheter assembly.

Define and lock the reflow temperature, dwell time, shrink tubing selection, and liner tension for each product design, then treat any change as a formal process change. Match heat and pressure to the thinnest liner wall in the design, not the average, since the thinnest point fails first. Controlled cooling matters as much as controlled heating because rapid cooling creates the thermal mismatch stress that later shows up as wrinkling or delamination.

6. Statistical Process Control (SPC)

Statistical process control is used to detect process drift before it results in defects. Track key parameters such as liner ID, wall thickness, peel force, and friction values on control charts, and respond to trends rather than waiting for out-of-spec results.

SPC also quickly reveals batch-to-batch material variation, as resin changes appear as shifts across all charts. Over time, this data identifies stable process steps and those requiring tighter control.

Hydromer®: Your Trusted PTFE Liners and Hydrophilic Coating Manufacturer

Every defect covered in this article becomes cheaper to solve when the liner is made right the first time. Hydromer®, Inc. brings 40+ years of experience in advanced hydrophilic coatings and PTFE liner manufacturing, with quality systems built to control dimensional, surface, and material defects at the source.

Our PTFE Liner Products include:

• MatrixLiner® Free Extruded Liner
• MatrixLiner® Extruded OTW Liner
• MorphoLiner® Casted OTW Liner

We are a trusted partner to leading medical device manufacturers. Our PTFE liners are fully customized to meet the specific dimensional, performance, and regulatory requirements of your catheter project.

Top 5 Advantages of Choosing Hydromer®, Inc. PTFE Liners

Hydromer® employs three advanced processes to manufacture ultra-thin-wall PTFE liners: Free Extrusion, Over-The-Wire (OTW) Mandrel Extrusion, and Film Casting. The process is selected according to your catheter design and requirements to help ensure defect-free liners.

Below are the top five benefits of selecting Hydromer® PTFE liners:

• Defect Control at the Source: Hydromer’s production lines enable precise micro-dimensional extrusion with tight control over wall thickness, concentricity, and inner diameter. Advanced in-line quality inspection catches dimensional and surface defects before liners ever ship.
• Certified Quality Systems: Hydromer® manufactures under ISO 13485:2016 and ISO 9001:2015 certified processes with full lot-level traceability. Each liner batch can be traced back to its resin batch, supporting fast root cause analysis when you need it.
• High-Quality Raw Materials: Hydromer uses premium fluoropolymer resins to minimize material voids, contamination, and batch-to-batch variation. Consistent input materials mean consistent liner behavior across every production lot.
• Consistent Output: Hydromer uses scalable production lines and technology to ensure reliable dimensional accuracy across high-volume runs. The same liner quality you validated during development is the quality you receive in production.
• Vertical Integration: Hydromer offers engineering support, design for manufacturability, material modification, prototyping, testing, validation, and manufacturing services. We also offer complimentary products, such as hydrophilic medical device coatings and friction testing machines that verify lumen lubricity in your own lab.

Get in Touch

Preventing PTFE liner defects begins with manufacturing liners correctly from the outset. Hydromer’s PTFE liners, hydrophilic coatings, coating equipment, and contract services support your product and production requirements.

Contact our engineering team to request samples of our custom MatrixLiner® Extruded OTW Liners.

Frequently Asked Questions