Softgel Vs. Hard Capsule in Liquid Capsule Filling: Which Is Right for Your Product?

Liquid-filled capsules have become increasingly popular in the pharmaceutical and health supplement industries. Compared with traditional powder-filled capsules, liquid formulations often offer higher bioavailability, better dose uniformity, faster dissolution, and improved patient compliance. They are especially suitable for poorly water-soluble active ingredients, oils, and self-emulsifying drug delivery systems (SEDDS).

When developing a liquid-filled capsule product, manufacturers are usually faced with an important decision: Should the formulation be filled into a softgel or a hard capsule? This article is to provide a comprehensive comparison of softgel and hard capsule in liquid filling technologies to help you determine which solution best fits your product.

1. Softgel vs. Hard Capsule: What's the Difference?

The capsule shell design determines not only how the liquid is encapsulated, but also which equipment can be used, how the sealing process is performed, and what types of formulations can be filled. These differences directly influence production efficiency, formulation compatibility, and investment.

Therefore, understanding the capsule structure and manufacturing principle provides the foundation for evaluating their liquid capsule filling processes and determining which types of liquid formulations are best suited for each capsule system.

1.1 Capsule Structure

The most obvious difference between softgels and hard capsules lies in their shell construction and materials.

A softgel is a one-piece, hermetically sealed capsule with a soft and flexible shell. During manufacturing, the shell is formed and sealed around the liquid fill in a single operation. This seamless structure provides excellent resistance to leakage, oxygen ingress, and moisture penetration.

Traditionally, softgel shells are manufactured from gelatin, water, and plasticizers such as glycerin or sorbitol, which give the shell its elasticity. To meet vegetarian, vegan, or religious requirements, manufacturers have also developed non-gelatin softgels using plant-based polymers such as modified starches or carrageenan.

A hard capsule, by contrast, consists of two separate components—a capsule body and a capsule cap. Empty capsules are manufactured in advance, and the liquid formulation is filled into the capsule body before the cap is locked and sealed. Because the shell contains a natural joint between the cap and body, an additional sealing process is generally required for liquid-filled applications to prevent leakage during storage and transportation.

Hard capsule shells have traditionally been made from gelatin, but HPMC (hydroxypropyl methylcellulose) and pullulan capsules have become increasingly popular in recent years. These plant-based materials offer advantages such as lower moisture sensitivity and are widely used for vegetarian products or moisture-sensitive formulations.

1.2 Manufacturing Principle

Softgels are manufactured using the Rotary Die Encapsulation process, which integrates capsule formation, liquid filling, and sealing into a single continuous operation. During production, molten gelatin is cast into two continuous ribbons that are guided into rotating die rolls. As the die pockets close, a metering pump injects a precisely controlled volume of liquid between the gelatin ribbons. The rotating dies then simultaneously shape, seal, and cut individual capsules, producing a hermetically sealed softgel in one step.

By contrast, hard capsules follow a two-stage manufacturing approach. The empty capsule shells are manufactured separately and supplied as finished two-piece capsules. During liquid filling, the capsule body and cap are first separated, the liquid formulation is dosed into the capsule body, and the capsule is then closed and locked. Since a natural joint remains between the cap and body, an additional sealing operation is typically required to prevent leakage.

2. How Is Liquid Capsule Filling Achieved in Softgel and Hard Capsule?

Since the structural difference between softgel and hard capsule, liquid capsule filling process differs significantly. Softgel manufacturing relies on the softgel encapsulation machine equipped with gelatin ribbon casting systems, rotary dies, and an injection wedge. Liquid-filled hard capsules are produced using a liquid capsule filling and sealing machine, which integrates precision liquid dosing with capsule closing and sealing technologies.

Understanding how these two machines operate helps manufacturers select the most appropriate technology for their production needs.

2.1 Softgel Encapsulation Machine

Softgel liquid filling is carried out using a softgel encapsulation machine, commonly based on the Rotary Die Encapsulation process. Unlike capsule filling machine, this machine does not fill pre-made capsules. Instead, it manufactures the capsule shell, injects the liquid, and seals each capsule in a fully integrated process.

The encapsulation process can be divided into the following stages.

Step 1. Gelatin Preparation

The process begins with the preparation of the gelatin mass. Gelatin is mixed with purified water, plasticizers such as glycerin or sorbitol, and optional colorants or opacifiers in a heated melting tank. The mixture is vacuum-deaerated to remove trapped air bubbles and maintained at a controlled temperature to ensure stable viscosity before encapsulation. At the same time, the liquid is prepared in a separate holding tank and kept homogeneous through mixing or gentle heating if required.

Step 2. Gelatin Ribbon Formation

The molten gelatin flows from the tank into the spreader boxes, where it is evenly distributed onto two large, water-cooled rotating drums. As the drums rotate, the gelatin rapidly cools and solidifies into two continuous ribbons with precisely controlled thickness. Cooling air and temperature are carefully regulated to maintain ribbon uniformity, since variations in thickness can directly affect capsule strength, sealing quality, and appearance.

Step 3. Ribbon Alignment

After leaving the cooling drums, the two gelatin ribbons travel through a series of guide rollers toward the encapsulation zone. Before reaching the rotary dies, a very thin layer of food-grade lubricant is applied to the ribbons to prevent sticking to metal components during transportation and sealing. The two ribbons then converge from opposite sides of the machine with precise alignment, preparing for capsule formation.

Step 4. Precision Fill Injection

At the center of the machine is the injection wedge, one of the most critical components of the softgel encapsulation system. A high-precision metering pump continuously delivers the liquid formulation through channels inside the heated wedge. As the two gelatin ribbons pass on either side of the wedge, a precisely measured volume of liquid is injected between them. The pressure generated during injection causes the gelatin ribbons to expand into the cavities of the rotary dies, ensuring accurate fill volume and excellent content uniformity.

Step 5. Capsule Forming, Sealing and Cutting

Immediately after injection, the filled gelatin ribbons enter the rotary die section. The two counter-rotating dies contain precisely machined capsule-shaped cavities. As corresponding die pockets close together, heat and pressure simultaneously shape the capsule, hermetically seal the two gelatin ribbons around the liquid, and cut the finished capsule from the surrounding gelatin web.

Step 6. Capsule Ejection

After leaving the rotary dies, stripper rollers gently separate the newly formed softgels from the excess gelatin ribbon. The capsules are discharged onto a conveyor system, while the remaining gelatin web is collected for recycling or disposal according to the production process. At this stage, the capsules are fully sealed but remain soft because of their relatively high moisture content.

Step 7. Drying

Fresh softgels undergo a two-stage drying process. They are first transferred into tumble dryers, where gentle rotation combined with high-volume airflow removes surface moisture and prevents capsules from sticking together. The capsules are then spread onto drying trays or moved into controlled drying tunnels or rooms, where temperature, humidity, and airflow are regulated until the shell reaches its final moisture content and mechanical strength.

2.2 Liquid Capsule Filling and Sealing Machine 

Unlike softgel manufacturing, a liquid capsule filling and sealing machine does not produce the capsule shell itself. Instead, it fills liquid formulations into pre-manufactured hard capsules and then seals the capsule joint to prevent leakage.

NJY-1000C Liquid Capsule Filling Machine from Rich Packing

A typical liquid capsule filling and sealing process includes the following stages.

Step 1. Capsule Feeding and Separation

The process begins with automatic capsule feeding. Empty capsules are loaded into the hopper and oriented before entering the capsule filling machine. A vacuum separation system then separates the capsule cap from the capsule body while keeping both parts accurately positioned in dedicated holders.

Depending on the capsule material, such as gelatin, HPMC, or pullulan, the separation force and vacuum level are carefully controlled to avoid capsule deformation or damage while maintaining stable high-speed operation.

Step 2. Capsule Inspection and Rejection

Before the capsules proceed to liquid filling, many liquid capsule filling machines incorporate an automatic inspection and rejection station.

Sensors monitor key production parameters such as

• Missing capsule bodies
• Missing capsule caps
• Improper capsule separation

Any defective capsule is automatically rejected before entering the downstream sealing process. This early rejection not only improves final product quality but also prevents sealing adhesive contamination and reduces unnecessary material waste.

Step 3. Precision Liquid Filling

After inspection, the capsule body moves to the filling station. The liquid formulation is supplied from a temperature-controlled hopper to maintain stable viscosity throughout production. According to the formulation characteristics, the machine may be equipped with:

• Ceramic piston pumps for high-precision volumetric dosing
• Peristaltic pumps for sterile or sensitive formulations
• Servo-driven metering pumps for high-speed production

Each filling nozzle dispenses a precisely controlled volume of liquid into the capsule body. The synchronization between capsule indexing and pump movement ensures excellent fill-weight accuracy while preventing dripping or contamination around the capsule rim.

Step 4. Capsule Locking

The capsule cap is accurately repositioned onto the filled capsule body. A locking mechanism then presses the two capsule halves together until the locking rings engage securely. At this point, the capsule has sufficient mechanical strength for handling, but the joint between the cap and body is not yet completely liquid-tight, especially for oil-based or low-viscosity formulations.

Step 5. Capsule Sealing

The locked capsules enter the sealing station, where a gelatin-based sealing solution (or an HPMC-based sealing solution for vegetarian capsules) is applied uniformly around the junction between the capsule cap and body.

The sealing solution is maintained at an elevated temperature, typically 40–60°C, to ensure appropriate viscosity and good wetting of the capsule surface. As the capsules rotate through the sealing station, a thin continuous band of warm sealing solution completely surrounds the capsule seam, filling microscopic gaps between the two shell halves and creating a continuous sealing ring after drying.

Step 6. Air Drying

Immediately after sealing, the gelatin band still contains a relatively high amount of moisture and has not yet developed its final mechanical strength. The capsules therefore enter a forced-air drying system, where carefully controlled airflow, temperature, and humidity accelerate moisture evaporation from the sealing band without overheating the capsule contents.

NYJ-330C Liquid Capsule Filling Machine from Rich Packing

3. Choosing the Right Capsule for Sealing Machine

Selecting the appropriate capsule depends largely on the physical and chemical characteristics of the liquid formulation.

Important considerations include:

• Viscosity
• Volatility
• Oxidation sensitivity
• Moisture sensitivity
• Thermal stability
• Filling accuracy requirements
• Shelf-life expectations

3.1 Suitable Liquids for Softgel

Softgels can accommodate a wide range of liquid and semi-solid formulations. Typical formulations include:

• Fish oil
• Omega-3 oils
• Vitamin E
• Plant oils
• Suspensions containing fine particles
• Semi-solid pastes
• High-viscosity gels
• Self-emulsifying drug delivery systems (SEDDS)

Because softgels are sealed immediately during encapsulation, they are particularly suitable for:

• Oxygen-sensitive formulations
• Easily oxidized oils
• Highly volatile ingredients
• Moisture-sensitive formulations
• High-viscosity materials
• Formulations requiring excellent leak protection

3.2 Suitable Liquids for Hard Capsule

Liquid-filled hard capsules are generally better suited to formulations with moderate viscosity and good flowability. Typical formulations include:

• Medium- and low-viscosity oils
• Liquid nutraceuticals
• PEG-based formulations
• Melted lipid formulations
• Melted wax formulations
• Self-emulsifying systems (SEDDS/SMEDDS)
• Pharmaceutical solutions

4. Production Scenarios for Two Types of Liquid Capsule Filling

For a broader station-level overview of hard-capsule production, see this capsule filling machine working principle guide.

For small-batch liquid-filled hard-capsule projects, compare the CGN-208L Liquid Capsule Filling Machine.

The choice between softgel and hard capsules in liquid capsule filling is not determined solely by the formulation itself. Manufacturers should also consider production scale, development stage, equipment availability, investment budget, and commercialization strategy.

5. Conclusion

In general, softgel encapsulation remains the preferred solution for large-scale commercial manufacturing, particularly for oil-based formulations, highly viscous liquids, and products requiring superior sealing performance, excellent moisture and oxygen protection, and an attractive appearance.

Liquid-filled hard capsules, on the other hand, offer greater manufacturing flexibility. By combining precision liquid dosing with capsule sealing technology, they enable manufacturers to produce a wide range of liquid formulations. This makes them particularly suitable for R&D, clinical trials, pilot production, small- to medium-scale manufacturing, and facilities that frequently switch between products or formulations.

Ultimately, there is no universal “best” technology, only the technology that best matches your formulation and manufacturing strategy. Understanding the differences in capsule structure, production process, formulation compatibility, and application scenarios allows manufacturers to make informed decisions that improve product quality, production efficiency, and long-term return on investment. As liquid dosage forms continue to gain popularity in both pharmaceutical and nutraceutical markets, selecting the right capsule technology will remain a key factor in achieving reliable, efficient, and competitive production.

6. FAQs

1. Can hard capsules be filled with liquid?

Yes. Liquid-filled hard capsules are specifically designed for oils, herbal extracts, lipid formulations, and other liquid or semi-liquid products. After filling, the capsules are sealed using technologies such as band sealing to prevent leakage.

2. What types of liquids are suitable for softgels?

Softgels are well suited for oils, high-viscosity liquids, semi-solids, suspensions, and oxygen- or moisture-sensitive formulations. Their one-piece hermetic structure provides excellent protection against leakage and oxidation.

3. Can heat-sensitive liquids be filled into hard capsules?

Yes. Most liquid-filled hard capsules are sealed with a warm gelatin or HPMC sealing band applied only to the capsule seam, minimizing heat exposure to the formulation. However, extremely heat-sensitive ingredients should always be evaluated through compatibility testing before production.

4. Do liquid-filled hard capsules require additional sealing?

Yes. Unlike softgels, hard capsules consist of two separate shell halves, so an additional sealing process is necessary after filling. This improves leak resistance, product stability, and shelf life.

5. Is a softgel encapsulation machine the same as a liquid capsule filling machine?

No. A softgel encapsulation machine forms, fills, and seals capsules in one continuous process. A liquid capsule filling machine fills pre-made hard capsules and then closes, seals, and dries them in separate production stages.