Empty hard capsules are made in two pieces: a cap and a body. Each shell is formed on a separate set of metal pins, dried, stripped from the pins, trimmed, and then joined in a pre-locked position. In broad terms, the process moves through seven stages: preparing the film-forming system, dipping the pins, distributing and drying the film, stripping and trimming the shells, joining the cap and body, inspecting the capsules, and packaging the released batch.
Knowing the sequence is useful. For a buyer, however, the real value lies in understanding what those steps can affect: shell dimensions, moisture balance, cap-body fit, appearance, packaging condition, and performance on the filling line.
The empty capsule manufacturing process at a glance
| Stage | What happens | Why it matters to a buyer |
|---|---|---|
| Material and solution preparation | The film-forming material, water, color system, and any product-specific processing aids are prepared into a controlled system. | Material identity, concentration, viscosity, filtration, and batch records establish the starting conditions for consistent shells. |
| Pin dipping and film formation | Separate cap and body pins enter the film-forming system and carry a thin wet film on their surfaces. | Dipping conditions and pin condition can influence wall distribution, dimensions, and visible defects. |
| Rotation and controlled drying | The wet film is distributed around the pins and dried under controlled conditions. | Drying affects shell strength, flexibility, moisture, dimensions, and stripping behavior. |
| Stripping and trimming | The dried cap and body shells are removed from the pins and cut to the required length. | Edge condition and shell length affect separation, closing, and visual quality. |
| Joining and pre-locking | The cap and body are aligned and partially joined for transport and later separation on a filling machine. | Cap-body fit and the pre-lock position influence feeding, opening, and final locking. |
| Inspection and optional printing | Capsules are checked against the applicable appearance, dimensional, and functional requirements. Printing may be added when specified. | Defect criteria, inspection records, color approval, and print checks support batch review. |
| Packaging and release | The capsules are packed for storage and transport, then released against the applicable specification. | Packaging integrity, storage instructions, COA data, and traceability remain important after production. |
1. Everything starts with the film-forming system
The first step takes place before a capsule shape is visible. The manufacturer prepares a system that will coat the forming pins evenly and produce shells with the required strength and dimensions after drying. Gelatin, HPMC, pullulan, and starch-based materials do not share one universal formula or processing window.
Typical controls include raw-material identity, concentration, viscosity, temperature, mixing time, filtration, deaeration, color dispersion, and holding time. The exact formulation and process parameters belong to the specific product and its validated manufacturing system. A public process diagram cannot replace those records.
2. Capsule size starts with the forming pins
Two-piece hard capsules are formed on shaped metal pins. One set forms the cap; another forms the body. The tooling is matched to both the capsule size and the geometry of each shell section.
When the pins enter and leave the film-forming system, a wet film remains on their surfaces. The condition of the solution, dipping depth, withdrawal, rotation, and pin surfaces can affect wall distribution, the closed end of the shell, and later stripping. Capsule size is therefore built into the tooling and process rather than assigned after the shells have been made.
3. Drying is about balance, not maximum dryness
After dipping, the coated pins rotate or move through a controlled sequence so the wet film can distribute before and during drying. The goal is not to remove as much moisture as possible. It is to reach the required balance of strength, flexibility, dimensions, and moisture for that capsule system.
Too much moisture can contribute to softening, deformation, or sticking. Too much moisture loss can increase brittleness in some capsule systems. Material, packaging, storage, and the filling-room environment can all influence shell condition after the capsules leave the production line.
4. From dry film to a pre-locked capsule
Once the films have enough strength, the cap and body shells are stripped from their pins. Each section is trimmed to the required length before the two pieces are aligned and joined.
Empty capsules are normally supplied in a pre-locked position. The connection must hold during packaging, transport, and feeding, yet still allow the filling machine to separate the cap from the body. Edge condition, shell length, diameter, and cap-body fit all matter at this stage.
5. Inspection and printing are separate control points
Depending on the product specification, inspection may cover visible defects, color, dimensions, and closing condition, along with other relevant attributes. Printing, if specified, introduces additional checks for text or logo accuracy, position, color, adhesion, and mix-up prevention.
Appearance alone does not define a finished batch. Buyers may also need the applicable specification, COA, batch identification, packaging information, storage conditions, and traceability records. The StellarCaps quality assurance page explains how quality documents support supplier review, while the guide to empty capsule quality control and batch traceability goes into more detail.
Do gelatin and HPMC follow the same process?
Gelatin and HPMC empty capsules share the same broad two-piece manufacturing logic: prepare a film-forming system, form the cap and body on separate pins, dry the films, strip and trim the shells, join the two pieces, inspect them, and package the released batch. The material behavior behind those steps is different.
Empty gelatin capsules use gelatin, a protein derived from animal collagen, as their main film-forming material. HPMC empty capsules use hypromellose as the main film-forming material. Depending on the product, an HPMC system may use a gelling system or a thermal-gelation route. Solution preparation, temperature control, film formation, drying, and moisture targets must therefore follow the specific capsule system.
Where manufacturing quality shows up during filling
A buyer does not need every confidential process parameter to evaluate a sample. Several manufacturing outputs, however, become visible on the filling line:
- Feeding and separation: capsules should orient and separate consistently on the intended equipment.
- Cap-body fit: the pre-lock should protect the empty capsule while still allowing controlled opening.
- Closing: dimensions, edge condition, fill level, and powder at the joint can all affect final locking.
- Brittleness or sticking: capsule condition should be reviewed together with storage, packaging, room humidity, fill material, and handling.
- Appearance: defect definitions, sampling, color standards, and print approvals should be agreed before acceptance criteria are set.
A filling problem should not automatically be assigned to the shell. The capsule batch, fill material, machine setup, environment, storage exposure, and timing of the observation all belong in the investigation.
What evidence should a buyer ask for?
For an initial supplier review or sample request, the following information is more useful than a process illustration on its own:
- the exact capsule material and size;
- the current product specification and a representative COA;
- relevant shell dimensions, closed length, and weight information;
- storage and packaging instructions;
- color and printing approval details, if required;
- batch identification and the traceability approach;
- change-notification and complaint-handling expectations; and
- samples for filling and packaging evaluation.
The available evidence will vary by product, supplier, and destination market. Buyers should request current documents for the exact material and specification under review rather than relying on a generic capability statement.
Frequently asked questions
Are “empty capsules” and “hollow capsules” the same thing?
In some supplier listings, hollow capsules refers to unfilled two-piece capsule shells. Empty capsules or empty hard capsules is clearer in international technical and purchasing communication.
Are empty hard capsules molded as one complete piece?
No. A standard two-piece hard capsule has a separately formed cap and body. The pieces are joined after drying and trimming, then separated and closed again during filling.
Does a manufacturing-process page prove a supplier's capability?
No. A public process description explains general manufacturing logic. Supplier capability should be supported by current product documents, samples, batch evidence, audit information where applicable, and performance on the buyer's intended filling and packaging process.
Why can an empty capsule become brittle or sticky after production?
Capsule shells continue to exchange moisture with the fill material, package, and surrounding environment. Packaging damage, unsuitable storage humidity, temperature changes, prolonged open-bag exposure, and the filling-room conditions can all change shell behavior.
Request samples or discuss a quotation
To request samples, ask for a bulk quote, or get a specification sheet, use the StellarCaps contact page and share the required material, capsule size, target fill weight, quantity, color, printing, packaging format, destination market, and document requirements. A defined project brief makes it easier to review the relevant product options and supporting documents.