Capsule formulation can use powders, granules, pellets or mini-tablets, each with unique pros and cons. Powders are simple and common but can be dusty or poorly flowing. Granules (agglomerated powders) improve flow and reduce dust at the cost of extra processing. Pellets are roughly spherical multi-unit particles with excellent flow and are ideal for controlled-release and combination formulations. Mini-tablets (tiny tablets filled into a capsule) allow precise dosing and multiple APIs or release profiles in one capsule. The choice of fill material affects mixture uniformity, dose flexibility and flowability – and it influences which capsule-filling machine features are needed.
This guide compares each form, shows how material choice matters for production, and even provides a decision tree to help you pick the best capsule fill material for your product (and thus the right equipment). We also list the key formulation data to share with capsule machine suppliers when scoping your project.
Hard capsules can be filled with a variety of solid forms. Here is a quick comparison of powder, granules, pellets and mini-tablets in capsules:
| Fill Material | Typical Form | Main Advantages | Common Challenges |
| Powder (fine particles) | Dry mix of API + excipients | High dosing flexibility; rapid dissolution (immediate release); simple formulation. | Flow issues: tends to clump, segregate or bridge; dose uniformity can suffer. Sensitive to moisture and static. |
| Granules (agglomerated powder) | Larger clusters from wet/dry granulation | Better flowability and bulk density; reduced dust; more uniform fill weight. Enables cohesive dosing. | Extra process steps: granulation adds cost/time. Particle size variation affects uniformity; bridging still possible if poorly dried. |
| Pellets (spheroids) | Rounded micro-beads (often coated) | Controlled release: can coat each pellet for timed release. Uniform shape → very good flow in hoppers. <br>Consistent dosing: measured by volume, not count. | Complex production: require granulation/extrusion and coating. Equipment must handle small beads without segregation. |
| Mini-Tablets (micro-tablets) | Tiny tablets (2–4 mm dia) | Flexible dosing: mix multiple mini-tablets for multi-API or staggered release. Easy to handle like small tablets. | Counting challenge: need special feeder to count and drop. May have lower flowability than loose beads. Requires precise tablet press tooling. |
Each material can be the primary fill or part of a combination. Modern capsule lines can even mix forms in one capsule (e.g. pellets + powder) to achieve complex release profiles.
The physical properties of your fill material directly affect capsule-filling performance and product quality. Flowability, particle size, density and moisture are key factors. For example, very fine powders may be cohesive or dusty (tending to clump or hang up on surfaces), whereas larger particles or pellets flow more easily. The choice also affects blend uniformity – fine powders with mixed particle sizes can segregate during handling, whereas uniform pellets or mini-tablets reduce that risk.
Fill material also drives dose precision and formulation flexibility. Pellets (often called “multiparticulates”) enable complex release patterns and the combination of different pellets in one capsule. Mini-tablets allow multiple APIs or coatings per capsule. In contrast, a simple powder blend usually delivers one release profile. Many capsule machines allow mixing different forms, but each addition (e.g. pellet + powder) adds complexity and may require separate feeders or stations.
Finally, the material dictates which dosing mechanism on the capsule-filler is used. Auger or disc feeders and tamping pins work well for free-flow powders, while pellet or tablet stations handle rigid particles. We cover these machine considerations below.
Powder is the classic capsule fill. It’s simply a free-flowing blend of API and excipients (diluents, glidants, etc.). Powders shine when you need simple, immediate-release formulas or highly customizable doses. Because powders have high surface area, they dissolve quickly — ideal for fast onset of action. And powders let you fine-tune a dose: for pediatrics, geriatric or variable strengths, you can adjust the mix easily.
However, powders come with drawbacks. Flowability is often poor: fine particles can bridge in hoppers or stick in feeders. Even well-blended powder can segregate (heavier particles settle) if shaken, causing fill-weight variation. The lack of a defined shape means dosing relies on volumetric or tamping methods (discs, vacuum/air) that demand very consistent powder behavior. As GMP Insiders notes, “powders often have poor flowability, making them difficult to handle”, which can lead to dosing issues. Moist or static-prone powders clump, causing some capsules to overfill and others underfill. Finally, powders can taste bad or irritate, since they release instantly; encapsulation or coatings can mask taste, but powders themselves offer limited protection.
When to choose powder: Formulations that call for immediate release, high-dose APIs (easy fill weight), or maximal flexibility. For low-dose potent drugs, powders can be tricky without granulation. Lab and R&D scales often use powders. For example, Jinlu’s NJP-400C capsule filler (24k capsules/hr) is designed for powders and granules, using tamping pins or dosing discs for precise fill weight.
Tips: Control particle size and moisture. Use glidants (e.g. Mg stearate) to improve flow. Keep the blend uniform and conduct powder flow studies. High-speed lines should track fill weight trends; common causes of variation include humidity changes, segregation and worn dosing discs.
Granules are simply powder particles bonded into larger granules (wet or dry granulation). By making particles bigger and more uniform, granulation dramatically improves flow and handling. The granule’s larger mass means it empties hoppers more consistently, and there is less dust. This leads to more stable fill weight and less machine downtime. GMP Insiders confirms that “granules offer improved flow properties and compressibility” over powders. Granules are also great intermediates if you eventually compress tablets: capsules can be a quick dose, while granules are also compressible.
Pellets (below) are essentially spherical granules. But even uncoated granule masses help for uniform filling. For manufacturers, granulation adds an extra step, but it often pays off by eliminating bridging. A fluid-bed or high-shear granulator can produce granules that dramatically cut segregation. (After granulation, you may screen to size to ensure uniform feed into the capsule fill hopper.)
When to choose granules: Use granules when the base powder is sticky, cohesive or has a wide size distribution. Granulation ensures consistent capsule weights especially on high-speed lines. Granules can also incorporate binders or coatings. For moderate release control, you might coat granules as mini-pellets.
Tips: Optimize granule size (usually a few hundred microns) for your filler’s hopper. Ensure granules are fully dried and free-flowing. Vibratory feeders or augers often feed granules reliably, and capsule fillers with volumetric granule dosing (e.g. segmented hoppers) handle them well. Jinlu’s capsule fillers accommodate granules: the NJP-400C, for instance, is rated for powders and granules.
Pellets (or spheroids) are small, rounded particles — often 0.5 to 2 mm in diameter — usually produced by extrusion-spheronization or layering techniques. Each pellet can be coated to control release (enteric, delayed, controlled, etc.), so pellet-filled capsules are ideal for multiparticulate and modified-release formulations. As Jinlu notes, “pellets are small spherical multi-unit beads, often coated for sustained release”. Capsules filled only with pellets (also called multi-particulate capsules) can give precise, predictable release: some pellets dissolve immediately, others later. This multi-phase release profile is hard to achieve with uniform powders.
Pellets flow very well due to their shape. A quick tilt of the hopper and pellets pour out smoothly into a dosing disc or rotating star-wheel feeder. Modern fillers often have segmented powder discs for volumetric pellet filling, or even turret hoppers that meter pellets by volume. Because pellets are relatively heavy and coarse, there’s very little dust, and machines run fast — up to tens of thousands of capsules per hour.
When to choose pellets: When you need controlled release or want to minimize dose variation. Pellets let you combine immediate- and extended-release pellets in one capsule to create different or staged drug-release profiles. They’re excellent for high-dose drugs that benefit from sustained release. Also, if your formula can handle the extra processing (extrusion, layering, or coating), pellets can outperform powders in consistency.
Tips: Match pellet size to the capsule filler. Large pellets may reduce count per capsule; too many small pellets may cause segregation in the hopper. Calibrate the volumetric feeder — since pellets fill by volume rather than count, accurate star-wheel settings are key. Check that pellets are not friable (dust). Jinlu’s specialized multi-particulate filling technology (available on machines like the NJP-1500D) handles pellets reliably and can accommodate multiple pellet sizes.
Mini-tablets (sometimes called micro-tablets) are tiny compressed tablets, typically 2–4 mm in diameter. Think of putting one or more of these very small tablets inside a larger hard capsule. This approach blends the benefits of tablets and capsules: each mini-tablet can contain a precise dose or different API, and can be coated for tailored release. For example, a capsule might contain one immediate-release mini-tablet of Drug A and one sustained-release mini-tablet of Drug B. Jinlu’s guide explains that mini-tablets “lets manufacturers combine different drugs, doses, or release profiles in one unit”.
Mini-tablets have excellent dose flexibility. Because they are compressed units, you can count them like tablets: one capsule = 5 tablets or 10 tablets, etc. This makes adjusting total dose easy. They also minimize segregation because each mini-tablet holds a fixed composition. Compared to pellets, mini-tablets often have lower porosity (less moisture sensitivity) and consistent tablet weight. A study notes that multi-unit forms (granules, pellets, mini-tablets) “offer efficient control of drug release” with “smaller inter- and intra-variability”.
On the flip side, feeding mini-tablets requires special equipment. Capsule fillers need a tablet-dosing station: typically a vibrating or rotating disk with pockets that count and drop each mini-tablet into the capsule body. This adds complexity and cost. Also, because mini-tablets are solid, they flow like granules but can jam if not handled gently. However, modern capsule fillers (including Jinlu’s machines) offer optional mini-tablet feeders. Indeed, Jinlu specifies that the NJP-400C accepts “micro tablet” fills, meaning it can feed pre-made mini-tablets.
When to choose mini-tablets: When you need precise dose combinations or want to include multiple APIs or release rates in one capsule. They are popular for pediatric or multi-drug products, where dose titration is key. Use mini-tablets if your formulation is tablet-friendly and you can afford the extra filling station. They shine when uniformity and fixed dosing are paramount.
Tips: Ensure all mini-tablets are consistent in size and hardness. Validate the tablet feeder with your specific mini-tablet shape. If using coated mini-tablets, handle them gently to avoid chipping. Combining mini-tablets with pellets or powder in one capsule is possible — just program the filler sequence (drop tablets, then add pellets, then top with powder, etc.) as Jinlu describes.
Sometimes the best solution uses more than one material. Multi-component fills can give dual-release or combination therapies. Examples:
These combination strategies exploit the strengths of each form. It requires a filling line with multiple stations, but many high-end machines support this. The benefit is a true combination dosage form: better therapeutic control and fewer pills for the patient. For instance, an anti-inflammatory might be delivered as 2 immediate-release mini-tablets + 50 delayed pellets in one capsule.
Choosing the right fill depends on your key requirements: flowability, dose flexibility, release profile, handling, and equipment. The table below maps these factors to each material:
| Factors / Material | Powder | Granules | Pellets | Mini-Tablets |
| Flowability | Medium / Low (fine powders can bridge) | Good (larger size reduces bridging) | Very Good (smooth spheres) | Good (generally fine, but need gentle handling) |
| Dose Flexibility | High (blend ratios easily changed) | High (same as powder after granulation) | High (mix different pellet types) | Very High (count tablets for precision) |
| Modified Release | Limited (blend with excipients) | Possible (coated granules) | Excellent (coat each pellet) | Excellent (coat tablets or use different tablets) |
| Content Uniformity | Moderate (risk of segregation) | Good (granulation promotes uniformity) | Very Good (each pellet identical) | Very Good (counted doses) |
| Processing Cost | Low (simple mixing) | Moderate (granulation step) | High (extrusion + coating) | High (tablet compression + coating) |
| Capsule Filling Ease | Simple (standard tamping/disc) | Easier (flows smoothly) | Easy (volumetric fillers work well) | Complex (needs tablet counting station) |
| Best Use Cases | Immediate-release or simple formulas | Bridging powders/low-dust fill | Controlled-release/multiparticulate | Multi-API or precise dosing (e.g. combination therapy) |
Above factors guide the decision. For example:
The fill material fundamentally determines the dosing mechanism and machine setup:
In each case, consider dosing accuracy and feed consistency: dense powders might use tamping pins; fluffy powders may need vacuum or augers; pellets benefit from volumetric precision; mini-tablets rely on good pocket design. The machine’s metering parts must be chosen to match the fill type.
For example, the NJP-400C automatic capsule filling machine is built to handle powders, granules, pellets and mini-tablets. Its adjustable feeding system (pneumatic agitation, tamper, etc.) allows switching between these materials. Likewise, the high-speed NJP-1500D capsule filler covers the same range at up to 90,000 cps/hour.
Before choosing a capsule filler (or adjusting an existing one), examine these material properties:
Example: A low-dose potent drug (<10 mg) with poor powder flow is a classic case for either granulation or mini-tablets. A high-dose, moisture-sensitive vitamin (300 mg) might do fine as coated pellets to avoid hygroscopicity.
The key is to feed this data into your equipment choice. Jinlu recommends giving suppliers the product’s bulk density, Carr’s Index, particle size, moisture content, and desired output. This ensures the right dosing principle (tamping pin vs dosator) is selected.
Now that the formulation needs are clear, match them to equipment:
Example Decision Flowchart:
This simple flow says: identify your fill type, then pick the corresponding feed mechanism and machine. Along the way, keep material properties in mind. Ultimately, select the capsule filler that supports your material and throughput (Jinlu offers semi and fully automatic models to suit both R&D and full-scale production).
Even with the right machine, watch out for these common issues in capsule filling, and how to fix them:
Most problems trace back to material behavior vs. machine setting. The key is in-process monitoring. As an industry guide advises, watch for weight drift, check material for dust/bridging signals, and adjust one factor at a time. Keep detailed batch records: variations in particle size or moisture of raw materials often explain downstream issues.
When requesting a capsule filler quote, give the vendor as much formulation data as possible. Key information includes:
| Data to Provide | Why It Matters |
| Product & Dose: Target fill weight, capsule size (000–5) | Determines required fill volume and machine capacity. |
| Formulation Density: Bulk/tapped density, Carr’s index/Hausner | Indicates flow and compressibility. Helps choose auger pitch and predict fill uniformity. |
| Particle Size: Powder D50 or granule size range | Affects flow behavior and risk of segregation or bridging. |
| Flow/Texture: Free-flowing vs cohesive/sticky (and moisture content) | Signals need for special feeders (e.g. vibration, air fluidization) and whether compression will hold. |
| Unit Dosage: # of tablets or pellets per capsule (if applicable) | Ensures the machine’s dosing stations (tablet chute, pellet auger) are set up for the right count. |
| Output: Desired production rate (capsules/hour) | Matches filler speed (semi-auto vs rotary) to your throughput requirements. |
Providing these details lets suppliers recommend the right model and settings. For instance, Jinlu advises including Carr’s Index and moisture info so engineers can suggest features for poor-flow powders. The table above (inspired by industry best practices) should serve as a checklist when talking to vendors. Ask them how they handle any flag items (e.g. “my powder is very hygroscopic” or “I need to mix two different pellets”).
In summary, powder isn’t automatically best for capsule fills. Each option has trade-offs:
The right choice depends on your drug’s properties, target release profile, and production needs. Crucially, match your fill material to the capsule filling equipment. A good rule of thumb: plan your formulation first, then pick the machine, not the other way around.
Looking for a capsule filling solution? Jinlu Packing’s machines cover all these scenarios. Our NJP series machines can handle powder, granules, pellets and mini-tablets. Whether you need small-scale R&D runs or high-speed production, we can recommend the right model and tooling. Contact Jinlu to discuss your formulation and machinery needs – our experts can guide you to the ideal capsule filler for your powder, granule, pellet or mini-tablet formulation.
Hard capsules can hold a wide range of fills – not just powder. They can contain dry powders, granules, small pellets/beads, or even mini-tablets (plus, with special equipment, semi-solids or liquids). In practice, you often see multiparticulate fills like coated pellets or tablet-pellet mixes. As Jinlu notes, empty hard shells can hold powders, granules, pellets or small tablets, as well as suspensions or oils. The key is that your capsule filler must be set up for the specific form.
Granulation solves many powder woes. By agglomerating fine powder into larger particles, flowability and dosing become much more reliable. Granules pack more densely and flow smoother, preventing hopper bridging and dust. They also reduce segregation during feeding, giving more uniform capsule weights. So if your powder mix is “clingy” or has wide particle sizes, converting it to granules (wet or dry) is often the best fix. Use granules when you need stable filling performance.
Pellets (small beads) unlock advanced release profiles. Each pellet can be coated for delayed or extended release. A capsule full of coated pellets can deliver multiple drug-release phases (some pellets dissolve now, others later). Pellets also flow extremely well and eliminate blending issues (each capsule gets a consistent volume of pellets). In short, pellets are ideal for controlled-release formulations. They do require specialized pellet-feeding equipment, but Jinlu and others offer fillers optimized for them.
Yes – this is called the “tablet-in-capsule” approach. Mini-tablets (e.g. 2–4 mm) can be dropped into a capsule using a counting feeder. This lets you put precise, pre-compressed doses inside each capsule. You might have one or more mini-tablets in a capsule, possibly combined with other fill. Advantages include mix-and-match dosing (different drugs or release forms in one pill) and low variability. The trade-off is you need a capsule filler with a tablet-dosing station. Jinlu’s machines can handle mini-tablets (they list “micro tablet” in their spec).
Absolutely. Many formulations use combinations to achieve multi-phase release or combine APIs. For example, a powder for immediate effect plus coated pellets for sustained effect. The capsule goes through two fill steps: first pellets, then powder (or vice versa). The capsule machine just has multiple stations in series. Each station handles one form. Jinlu’s advanced fillers support this – you can “drop mini-tablets, then add pellets, then top off with powder” in one capsule. Just be mindful of how the materials interact (e.g. powder may settle into pellet gaps, which is fine if intended).
Fill variation usually comes from either the dosing mechanism or the material. Common culprits:
• Powder flow changes: moisture uptake, static, or fines can make the powder pack differently.
• Dosing misalignment: A worn disk or tamping pin delivers uneven doses.
• Segregation: Blend components settling differently (heavy particles vs light).
• Equipment factors: Star-wheel rate mismatched to auger, or hopper starvation when refill is delayed.
Fixes include: Calibrating and aligning the dosing disc or tampers; using agitators/vibrators in the hopper; maintaining consistent feed (avoid hopper going empty); conditioning the powder (drying, adding glidants, or granulating). Also run in-process checks (e.g. check capsule weights regularly during a run) to catch drift early.
Powder flow can be improved several ways:
• Add glidants/lubricants: A small % of magnesium stearate or colloidal silica coats particles and reduces inter-particle friction.
• Granulate or agglomerate: As discussed, converting powder to granules drastically improves flow.
• Control humidity: Keep RH stable; some powders flow better when slightly humidified, others when dry.
• Particle size optimization: A narrow PSD (particle size distribution) avoids extreme fines. Sometimes milling the API helps.
• Machine adjustments: Use vacuum assist or change tamp depth. Ensure the hopper has proper vibration or paddle mixing.
Yes. Most high-end automatic capsule fillers have options for pellets and mini-tabs. For pellets, machines use special dosing disks or segmented hoppers. Jinlu explicitly lists pellet applications for their models (e.g. NJP-400C, NJP-1500D can fill “pellet” material). For mini-tablets, look for a machine with a tablet feeder. Jinlu’s product page notes “micro tablet” as applicable material, meaning those models have the tablet-dosing station available. In short, ensure the chosen model’s spec sheet or datasheet mentions pellet and mini-tablet capability.
Particle size influences flow and fill volume. Fine powders (300 µm) flow better but pack less densely (so more volume needed for same dose). Bulk/tapped density tells you how many capsules you need for a given dose. For example, a very low bulk density means your 500 mg dose might not fit in a size 3 capsule. Capsule fillers must be set up for the expected particle size or density; otherwise, capsule bodies could slip, clog, or break. Always characterize your blend’s density and size (as Jinlu recommends) before committing to a machine.
A multiparticulate capsule is one containing many small units (pellets, beads, mini-tablets) instead of a single mass of powder. These systems are prized for controlled release. Each unit can release drug independently, giving smoother kinetics. For example, a multiparticulate capsule with coated pellets can provide extended release with less risk of dose dumping. The term also covers combinations like pellets+pills in one capsule. It’s essentially an umbrella term for multi-unit dosage forms in capsules.
References：
1.Dosage Form Drug Manufacturers cGMPs (10/93) —— U.S. Food and Drug Administration
2.Mini-tablets versus pellets as promising multiparticulate modified release delivery systems for highly soluble drugs —— PubMed
3.A flexible technology for modified-release drugs: multiple-unit pellet system (MUPS) —— PubMed
4.The filling of powders into two-piece hard capsules —— ScienceDirect
5.The influence of pellet shape and film coating on the filling of pellets into hard shell capsules —— ScienceDirect
6.Role of Pellet Size, Shape, and Filling Method in Achieving Fill Weight Uniformity for Encapsulated Pelletized Systems: A Comparison of Experiment and Computer Simulation —— ScienceDirect
Petty Fu, Founder of Jinlupacking, brings over 20 years of expertise to the pharmaceutical machinery sector. Under his leadership, Jinlu has grown into a trusted supplier integrating design, production, and sales. Petty is passionate about sharing his deep industry knowledge to help clients navigate the complexities of pharma packaging, ensuring they receive not just equipment, but a true one-stop service partnership tailored to their production goals.
