PTFE Packing is a workhorse sealing material in pumps, valves, and agitators across the chemical, pharmaceutical, food, and water industries. Buyers often see two product families on the same supplier shelf: pure PTFE packing and expanded PTFE packing. The two look similar, are both white, and are both described as chemically inert. But their material structure is fundamentally different, and that difference determines how they seal, how they wear, how they handle shaft runout, and how they perform at temperature. A buyer who treats them as interchangeable will select a packing that is either over-specified for the application or, more dangerously, under-specified for the service conditions.
This guide is written for procurement teams who source PTFE Packing and need to understand the structural difference between the pure and expanded forms. It explains the molecular and morphological difference, how the manufacturing process creates that difference, how the structure translates into sealing performance, which structural characteristics buyers should verify in a supplier's product data, and how the two structures compare in chemical and thermal resistance. The content is organized around the questions a buyer should ask, and it includes the product parameters and documentation that a reliable supplier should provide. Our factory at Ningbo Kaxite Sealing Materials Co., Ltd. produces both pure and expanded PTFE Packing, and the guidance below reflects the material science and procurement standards we apply to the products we supply.
Table of Contents
- 1. What Is the Fundamental Molecular Difference Between Pure PTFE and Expanded PTFE?
- 2. How Does the Manufacturing Process Create the Structural Difference?
- 3. Why Does the Structural Difference Affect Sealing Performance?
- 4. What Structural Characteristics Should Buyers Verify in a PTFE Packing?
- 5. How Do the Two Structures Compare in Chemical and Thermal Resistance?
- 6. Frequently Asked Questions (FAQ)
- 7. Conclusion
1. What Is the Fundamental Molecular Difference Between Pure PTFE and Expanded PTFE?
Pure PTFE and expanded PTFE are both made from the same polymer, polytetrafluoroethylene. The chemical repeat unit, the carbon-fluorine backbone, and the high crystallinity are common to both. The difference is not in the chemistry. It is in the morphology, the physical arrangement of the polymer chains and the voids between them. Pure PTFE packing is produced from skived PTFE film or from PTFE resin that is molded and then slit or shaped into a packing. The material is dense, with a low void content, and the polymer chains are oriented in the direction of the film or the molding flow. Expanded PTFE packing is produced by a process that stretches the PTFE under controlled conditions to create a microporous, fibrillated structure. The polymer chains are drawn into thin fibrils, and the spaces between the fibrils form a network of microscopic pores.
The table below summarizes the structural difference at the molecular and morphological level.
| Structural Feature | Pure PTFE Packing | Expanded PTFE Packing |
| Chemical composition | PTFE homopolymer | PTFE homopolymer |
| Morphology | Dense, oriented film or molded shape | Microporous, fibrillated network |
| Void content | Low, typically less than 5% | High, typically 50% to 80% |
| Polymer chain arrangement | Parallel orientation from film or flow | Fibrils with nodes and interconnected pores |
| Density | Approximately 2.1 to 2.2 g/cm³ | Approximately 0.6 to 1.0 g/cm³ |
| Surface | Smooth, non-porous | Textured, porous, compressible |
The structural difference is the reason the two packings behave differently in service. Pure PTFE packing is dense and dimensionally stable. It resists extrusion and creep, but it is relatively stiff and has limited compressibility. Expanded PTFE packing is soft, compressible, and conformable because the porous network allows the material to deform and fill the irregularities of the stuffing box and the shaft. This conformability is achieved without sacrificing chemical resistance, because the base polymer is the same. The buyer's decision therefore depends on the mechanical demands of the application, not on the chemical resistance of the polymer.
Our factory at Kaxite produces both pure and expanded PTFE Packing and maintains the material data that distinguishes the two structures. We provide the density, the void content, and the morphology description for each product so that buyers can match the packing to the application. The goal is to make the structural difference visible in the procurement data, not just in the marketing description.
2. How Does the Manufacturing Process Create the Structural Difference?
The manufacturing process is what creates the structural difference. Pure PTFE packing begins with a PTFE resin that is molded into a billet or a sheet. The billet is sintered, cooled, and then skived into a thin film. The film is slit into a tape, and the tape is braided or twisted into a packing. The sintering and skiving steps produce a dense, oriented material with a low void content. The polymer chains align in the direction of the skiving, and the resulting packing has a smooth surface and a high tensile strength in the machine direction. The process is essentially a densification process: the goal is to remove voids and to produce a uniform, non-porous structure.
Expanded PTFE packing begins with a similar PTFE resin, but the process includes a stretching step. The resin is mixed with a lubricant, preformed, and then stretched under controlled temperature and strain rate. The stretching draws the polymer chains into fibrils and creates a microporous network. The lubricant is removed, and the expanded tape is slit and braided into a packing. The process is a texturizing process: the goal is to create a controlled void structure that gives the packing its compressibility and conformability. The table below compares the process steps and their effect on the structure.
| Process Step | Pure PTFE Packing | Expanded PTFE Packing |
| Resin preparation | PTFE resin, no lubricant | PTFE resin mixed with lubricant |
| Preforming | Molded billet or sheet | Preformed billet for stretching |
| Stretching | Not applied | Controlled stretching creates fibrils and pores |
| Sintering | High-temperature sintering | Sintering after stretching to lock the structure |
| Forming | Skiving and slitting into tape | Slitting the expanded tape |
| Braiding | Braided or twisted into packing | Braided or twisted into packing |
| Resulting structure | Dense, oriented, non-porous | Microporous, fibrillated, compressible |
The process difference is not a minor variation. It is the reason the two products have different compression set, different recovery, and different leakage behavior. A pure PTFE packing that is braided from a dense film will resist extrusion but may not conform to a worn shaft. An expanded PTFE packing that is braided from a microporous tape will conform to the shaft and the stuffing box, but it may have lower tensile strength and may require a different installation technique. The buyer should ask the supplier to describe the process and the resulting structure, not just the chemical composition.
Our factory at Ningbo Kaxite Sealing Materials Co., Ltd. controls the stretching ratio, the sintering temperature, and the braiding tension to produce expanded PTFE Packing with a consistent pore structure. We also control the skiving thickness and the orientation for our pure PTFE Packing. The goal is to make the structure reproducible, so that the packing performs consistently from batch to batch.
3. Why Does the Structural Difference Affect Sealing Performance?
The structural difference affects sealing performance because the sealing mechanism depends on how the packing deforms under compression and how it recovers when the compression is released. A pure PTFE packing is dense and relatively stiff. When it is compressed in the stuffing box, it resists deformation and generates a high sealing stress against the shaft. It has good creep resistance and low permeability, which makes it suitable for high-pressure and high-temperature service. But it has limited conformability, so it may not seal well on a worn shaft or a misaligned stuffing box. An expanded PTFE packing is soft and compressible. When it is compressed, the porous network collapses and the material conforms to the shaft and the stuffing box. It has excellent conformability and low friction, which makes it suitable for low-speed, general-service applications and for shafts that are not perfectly smooth.
The performance differences are summarized in the table below.
| Performance Characteristic | Pure PTFE Packing | Expanded PTFE Packing |
| Compressibility | Low to moderate | High |
| Conformability to shaft | Moderate | Excellent |
| Creep resistance | Good | Moderate |
| Extrusion resistance | Good | Moderate |
| Friction | Moderate | Low |
| Shaft speed capability | Moderate to high | Low to moderate |
| Best application | High-pressure, high-temperature, chemically aggressive | General service, worn shafts, low-speed, food and pharmaceutical |
The practical consequence is that the two packings are not interchangeable. A pure PTFE packing may leak on a worn shaft because it cannot conform to the surface. An expanded PTFE packing may extrude or creep in a high-pressure application because its porous structure is less resistant to deformation. The buyer should match the structure to the application conditions, and the supplier should provide the compression, recovery, and creep data that support the selection. Our factory at Ningbo Kaxite Sealing Materials Co., Ltd. provides the performance data for both product families and can advise on the selection for a specific pump or valve.
4. What Structural Characteristics Should Buyers Verify in a PTFE Packing?
Buyers should verify the structural characteristics that determine whether the packing will perform in the intended service. The verification should include the density, the void content, the tensile strength, the compression set, the recovery, and the surface morphology. The table below provides a procurement verification checklist for PTFE Packing.
| Characteristic | Pure PTFE Packing | Expanded PTFE Packing | Why It Matters |
| Density | 2.1 to 2.2 g/cm³ | 0.6 to 1.0 g/cm³ | Indicates the void content and the compressibility |
| Void content | Low, less than 5% | High, 50% to 80% | Determines conformability and permeability |
| Tensile strength | High | Moderate | Affects installation and extrusion resistance |
| Compression set | Low | Moderate | Affects sealing stress retention |
| Recovery | Moderate | High | Affects the ability to follow shaft movement |
| Surface morphology | Smooth, non-porous | Textured, porous | Affects friction and conformability |
The verification should be supported by the supplier's test data. A supplier that provides only a chemical composition certificate is not providing the structural data that the buyer needs. A supplier that provides density, void content, compression set, and recovery data is providing the evidence that the packing will perform as specified. Our factory at Kaxite provides these data for both pure and expanded PTFE Packing, and we welcome customer audits to verify the manufacturing process.
For a buyer, the structural verification should be combined with an application review. The packing that is structurally correct for one application may be incorrect for another. The buyer should confirm the shaft speed, the pressure, the temperature, the fluid, and the shaft condition before selecting the structure. The supplier's technical team can help with this review if the buyer provides the application data.
5. How Do the Two Structures Compare in Chemical and Thermal Resistance?
The chemical and thermal resistance of pure PTFE and expanded PTFE packing is essentially the same, because both are made from the same PTFE polymer. Both resist attack by almost all chemicals, with the exception of molten alkali metals and certain fluorinating agents. Both have a continuous service temperature range of approximately -200°C to +260°C, with the exact limit depending on the grade and the application. The structural difference does not change the chemical resistance, but it does change the way the packing responds to thermal cycling and chemical exposure. A dense pure PTFE packing has a lower permeability, so it is less susceptible to chemical attack through the bulk of the material. An expanded PTFE packing has a higher surface area and a porous structure, so it may absorb more process fluid, but the PTFE itself remains inert. The table below compares the two structures in chemical and thermal terms.
| Property | Pure PTFE Packing | Expanded PTFE Packing |
| Chemical resistance | Excellent, inert to most chemicals | Excellent, inert to most chemicals |
| Permeability | Low | Higher due to porosity |
| Thermal conductivity | Moderate | Lower due to voids |
| Thermal cycling response | Dimensionally stable | Compressible, follows movement |
| Continuous service temperature | -200°C to +260°C | -200°C to +260°C |
| Best chemical application | High-pressure, low-permeability service | General chemical service, food and pharmaceutical |
The thermal performance is influenced by the structure in a subtle way. Pure PTFE packing has a higher thermal conductivity and a lower void content, so it dissipates frictional heat more effectively and is less prone to thermal degradation at the shaft contact. Expanded PTFE packing has a lower thermal conductivity and a higher void content, so it may run hotter at the shaft contact if the friction is not controlled. This is why expanded PTFE packing is often used at lower shaft speeds and with careful installation to avoid over-compression. Our factory at Ningbo Kaxite Sealing Materials Co., Ltd. provides the thermal and chemical resistance data for both structures and can advise on the selection for a specific process fluid and temperature.
For a buyer, the comparison shows that the chemical and thermal resistance is not the deciding factor between the two structures. The deciding factor is the mechanical behavior: the pure packing for high-pressure, high-stability service, and the expanded packing for conformability and low-speed general service. The buyer should make the decision on the mechanical requirements and use the chemical and thermal data to confirm that both structures are compatible with the process fluid.
6. Frequently Asked Questions (FAQ)
Question 1: Are pure PTFE packing and expanded PTFE packing made from the same polymer?
Answer: Yes, both are made from polytetrafluoroethylene. The chemical composition is the same. The difference is the physical structure: pure PTFE packing is dense and oriented, while expanded PTFE packing is microporous and fibrillated. The structural difference is created by the manufacturing process, not by a difference in the polymer chemistry.
Question 2: Which packing is better for a worn pump shaft?
Answer: Expanded PTFE packing is generally the better choice for a worn pump shaft because its porous, compressible structure conforms to the shaft surface and fills the irregularities. A pure PTFE packing is denser and stiffer, so it may not seal as effectively on a worn shaft. However, if the pressure is high, the pure packing may be preferred for its better extrusion resistance.
Question 3: Can expanded PTFE packing be used at high pressure?
Answer: Expanded PTFE packing can be used at moderate pressures, but its porous structure has lower extrusion resistance than pure PTFE packing. For high-pressure service, the pure PTFE packing is generally the better choice. The exact pressure limit depends on the packing size, the stuffing box clearance, and the installation technique. The supplier should provide the pressure rating for the specific product.
Question 4: Does the porous structure of expanded PTFE packing affect its chemical resistance?
Answer: The PTFE polymer itself remains chemically inert, so the chemical resistance is not compromised. However, the porous structure has a higher surface area and can absorb more process fluid than a dense pure PTFE packing. This may affect cleanability in food and pharmaceutical applications. The buyer should confirm that the packing is suitable for the cleaning regime of the process.
Question 5: What documentation should I request to verify the structure of a PTFE packing?
Answer: Request the density, the void content, the tensile strength, the compression set, and the recovery data for the product. For expanded PTFE packing, request the pore structure description and the stretching process data. For pure PTFE packing, request the skiving thickness and the orientation data. A supplier that provides these data is a supplier that can demonstrate the structural difference and support the selection.
7. Conclusion
Pure PTFE packing and expanded PTFE packing differ in material structure, not in chemical composition. Pure PTFE packing is dense and oriented, with low void content and high extrusion resistance. Expanded PTFE packing is microporous and fibrillated, with high void content and excellent conformability. The structural difference determines how each packing seals, how it responds to worn shafts and thermal cycling, and where it is best applied. For procurement teams, the key is to request the structural data, match the structure to the mechanical requirements of the application, and confirm the chemical and thermal compatibility. Our factory at Ningbo Kaxite Sealing Materials Co., Ltd. produces both pure and expanded PTFE Packing and provides the density, void content, compression set, and recovery data that buyers need to make the selection. If you are sourcing PTFE Packing for a pump, valve, or agitator, contact our team to discuss your application and to request the structural data for the products you are considering.
Contact Ningbo Kaxite Sealing Materials Co., Ltd. today to discuss your PTFE Packing requirements and to request the structural and performance data for pure and expanded PTFE Packing.