When medical, clinical or laboratory samples need to be transported, the packaging system matters. For many biological samples, the correct approach is not simply choosing a specimen bag or carrier in isolation, but understanding how each layer works together within the UN3373 Category B and P650 / PI650 packaging framework.
This guide explains the principle of UN3373 triple packaging, where 95kPa specimen bags fit, when absorbent pads are required, and how insulated medical carriers can be used as the outer packaging layer where temperature-controlled transport is needed.
Buyer note
This guide is intended as a practical overview of UN3373 triple packaging. It does not replace official transport guidance. The sender remains responsible for classifying the substance, selecting the correct packaging system and checking the latest ADR, IATA and carrier requirements.
UN3373 packaging at a glance
| Packaging layer | What it does | Typical product examples | Universeal supply position |
|---|---|---|---|
| 1. Primary receptacle | Holds the sample directly | Tube, vial, swab container, sample pot | Not supplied by Universeal, but important to the system |
| 2. Secondary packaging | Provides leakproof or siftproof containment around the primary receptacle | 95kPa specimen bag, UN3373 specimen transport bag, sample pouch | Supplied: ADR road transport bags, IATA air transport bag options, and standard specimen bag options for appropriate workflows |
| Absorbent material | Absorbs liquid if the primary receptacle leaks | Absorbent pad or absorbent sheet | Supplied: standard 50ml option and other absorbency levels available |
| 3. Outer packaging | Protects the consignment during handling and transport | Box, case, mailer or insulated medical carrier | Supplied: insulated medical carriers for temperature-controlled transport workflows |
The basic triple packaging principle
A UN3373 Category B packaging system is designed around three protective layers: the primary receptacle, the secondary packaging and the outer packaging. For liquid samples, absorbent material is also used between the primary receptacle and the secondary packaging.
Each layer has a different purpose. The primary receptacle contains the specimen. The secondary packaging contains the primary receptacle and provides an additional protective layer. The outer packaging protects the completed package during handling, movement and transport.
For buyers, the key point is simple: a specimen bag is not usually the complete packaging system on its own. It is one important component within a wider UN3373 / P650 packaging approach.
What is UN3373 packaging?
UN3373 is the transport classification used for Biological Substance, Category B. In healthcare and laboratory settings, this can include many routine diagnostic and clinical samples being transported between hospitals, clinics, laboratories, testing facilities and collection points.
| Sample type | Common transport context |
|---|---|
| Blood samples | Clinic, hospital, laboratory or diagnostic testing routes |
| Swab samples | Pathology, diagnostic or screening programmes |
| Urine samples | Healthcare, workplace testing or laboratory analysis |
| Stool samples | Clinical and diagnostic sample transport |
| Other biological specimens | Laboratory, veterinary, medical or research settings |
Not every biological sample is automatically treated the same way. Classification remains the responsibility of the consignor, and official guidance should always be checked.
What does P650 require in practice?
P650 is the packing instruction associated with UN3373 Biological Substance, Category B. For road transport, this is commonly discussed under ADR Packing Instruction P650. For air transport, IATA Packing Instruction 650 / PI650 is relevant.
Although the details depend on the transport mode, carrier and current regulations, the practical principle is that the sample should be protected by a complete layered packaging system.
For liquid biological substances
| Requirement area | Practical meaning for buyers |
|---|---|
| Primary receptacle | The sample container must be leakproof |
| Secondary packaging | The specimen bag or pouch must also be leakproof |
| Absorbent material | Absorbent material should be placed between the primary and secondary packaging |
| Absorbency level | Absorbent material should be sufficient for the liquid contents being transported |
| Multiple receptacles | Fragile primary receptacles should be separated or wrapped to prevent contact |
| 95 kPa pressure requirement | Either the primary receptacle or secondary packaging must withstand 95 kPa without leakage |
Why 95kPa matters
For liquid substances under P650, either the primary receptacle or the secondary packaging must be capable of withstanding an internal pressure of 95 kPa without leakage. This is why 95kPa specimen bags are commonly selected as the secondary packaging layer for UN3373 sample transport.
For solid biological substances
For solid samples, the primary receptacle and secondary packaging should generally be siftproof rather than leakproof. However, if there is any possibility of residual liquid, buyers should consider packaging suitable for liquids, including absorbent material.
Primary receptacles: the sample container
The primary receptacle is the first layer of the packaging system. This is the container that directly holds the specimen.
Examples include blood tubes, sample vials, swab tubes, stool sample containers, urine sample pots and other diagnostic sample containers.
Universeal does not supply primary receptacles, but they are important to understand because the performance of the overall packaging system starts here. The primary container should be appropriate for the sample type, properly closed, and suitable for the conditions of transport.
Where multiple fragile primary receptacles are placed inside one secondary packaging, they should be wrapped or separated so they cannot knock together, break, puncture the bag or leak during normal handling.
Secondary packaging: where 95kPa specimen bags fit
The secondary packaging is the layer around the primary receptacle. In many healthcare, pathology and laboratory sample transport systems, this is a leakproof specimen transport bag or pouch.
A 95kPa specimen bag helps provide a clear secondary packaging option within the wider UN3373 / P650 system. It is commonly used for medical, clinical, pathology and laboratory sample transport, particularly where liquid samples are involved.
| Buyer concern | How secondary packaging helps |
|---|---|
| Leakage from a primary receptacle | Provides an additional containment layer |
| Handler protection | Helps reduce exposure risk during transport and handling |
| Sample organisation | Keeps samples contained and identifiable during movement |
| Road or air transport requirements | Allows buyers to select ADR or IATA bag options depending on route |
| Practical dispatch workflow | Supports repeat clinic-to-lab, hospital-to-lab and courier collection routes |
Universeal supplies 95kPa ADR specimen bags for road transport and 95kPa IATA specimen bags for air transport for use within UN3373 Category B sample transport workflows.
Standard biohazard and urgent sample bags
Not every specimen transport workflow requires the same type of secondary bag. Alongside 95kPa specimen transport bags, some healthcare and laboratory teams also use standard biohazard specimen bags with document pouch or urgent sample specimen bags for routine handling, document separation and visual identification.
These bags can be useful for internal hospital workflows, routine pathology handling, separating paperwork from the sample compartment, identifying urgent samples and supporting specimen handling where the required containment performance is provided elsewhere in the packaging system.
Standard specimen bags vs 95kPa bags
Standard biohazard specimen bags and urgent sample bags are useful for routine sample handling, document separation and visual identification, but they should not be treated as a direct substitute for 95kPa specimen transport bags. For liquid substances under P650, either the primary receptacle or the secondary packaging must be capable of withstanding 95 kPa without leakage.
A non-95kPa specimen bag may be appropriate where the primary receptacle provides the required 95 kPa performance, or where the sample has been assessed as an exempt human or animal specimen and is packaged according to the applicable exempt specimen requirements.
If the sample is classified as UN3373 Biological Substance, Category B and the primary receptacle does not provide the required 95 kPa performance, a 95kPa specimen transport bag should normally be selected as the secondary packaging layer.
ADR road transport bags vs IATA air transport bags
A key buying decision is the transport route. A sample moved by road may have different requirements from a sample that may be moved by air.
| Transport route | Typical use case | Buyer consideration |
|---|---|---|
| ADR road transport | Clinic-to-lab, hospital-to-lab, courier rounds, regional healthcare logistics | Choose suitable road transport specimen bags and check ADR/P650 requirements |
| IATA air transport | Samples that may move by air, international routes or air-courier networks | Choose suitable IATA / PI650 specimen bags and check carrier requirements |
| Mixed or uncertain route | Courier networks where samples may transfer between modes | Check with the carrier before dispatch and avoid assuming road packaging is suitable for air |
As a practical rule, buyers should avoid assuming that a road transport specimen bag is automatically suitable for air transport. If samples may travel by air, it is sensible to choose an appropriate IATA specimen transport bag and confirm the latest requirements with the carrier.
Absorbent pads: small component, important role
Absorbent material is an important part of UN3373 packaging for liquid samples. It is placed between the primary receptacle and secondary packaging so that, if a tube, vial or container leaks, the liquid can be absorbed before it affects the rest of the package.
This is especially relevant for blood samples, urine samples, swabs with transport medium, liquid diagnostic specimens and multiple sample tubes placed into one specimen transport bag.
| Question | Why it matters |
|---|---|
| How much liquid is in each primary receptacle? | The absorbent material should be sufficient for the contents |
| Are multiple receptacles being packed together? | The total potential liquid volume may be higher |
| Is the sample route routine or higher-risk? | Repeated handling or longer routes may require more robust packaging choices |
| Is the absorbent pad being supplied separately or pre-packed? | Buyers need to know what is included in the pack |
Absorbency should match the sample volume
Absorbent material should be sufficient for the liquid contents being transported. Universeal can supply absorbent pads in different absorbency levels, including a standard 50ml option, but buyers should always match absorbency to the sample volume and packaging configuration.
Universeal can supply absorbent pads for UN3373 packaging in different absorbency levels, including a standard 50ml absorbent option.
Outer packaging: insulated medical carriers for temperature-controlled transport
The outer packaging layer provides the external protection for the consignment during handling and transport. Depending on the route, this may take the form of a box, case, mailer or reusable carrier.
For medical samples that need to be moved under temperature-controlled conditions, an insulated medical carrier can provide a practical outer packaging option. It helps protect the samples during collection, handling and onward transport while supporting temperature-controlled medical logistics workflows.
| Application | Why an insulated carrier may help |
|---|---|
| Clinic-to-laboratory transport | Supports regular sample collection and movement |
| Hospital-to-laboratory routes | Useful for repeat internal or external transport |
| Pathology collection rounds | Helps organise and protect samples during courier routes |
| Diagnostic sample movement | Supports structured medical logistics workflows |
| Temperature-sensitive samples | Helps support temperature-controlled transport requirements |
| Reusable healthcare logistics | More suitable than single-use outer packaging for repeated routes |
Temperature-controlled transport
An insulated medical carrier can provide a practical outer packaging option where samples need protection during handling and temperature-controlled transport. It should be used as part of a wider packaging system that includes suitable primary receptacles, secondary packaging and absorbent material where required.
An insulated medical carrier should not be treated as a substitute for correct primary and secondary containment. Instead, it forms the outer transport layer around the primary receptacle, secondary packaging and absorbent material.
For air transport, buyers should also check the specific IATA and carrier requirements for the outer packaging, including rigidity and marking requirements. For road-based healthcare logistics, an insulated carrier can be a practical solution where temperature control, repeat handling and route efficiency are important.
For temperature-controlled medical sample transport, Universeal supplies the SecureLab COOL insulated sample transport bag and SecureLab CHILL insulated medical carrier.
How the components work together
| Step | Packaging action | Product type |
|---|---|---|
| 1 | Seal the sample inside a suitable primary receptacle | Tube, vial, pot or swab container |
| 2 | Place the primary receptacle into secondary packaging | 95kPa specimen bag or UN3373 transport bag |
| 3 | Add absorbent material where liquids are being transported | Absorbent pad or absorbent sheet |
| 4 | Place the secondary package into outer packaging | Insulated medical carrier, case, box or other suitable outer packaging |
| 5 | Check route and marking requirements | ADR, IATA, carrier and UN3373 requirements |
| 6 | Dispatch through the chosen transport route | Road, air or courier network |
This layered approach is the reason buyers should avoid choosing products in isolation. The correct secondary bag is important, but it still needs to be used with the right primary receptacle, absorbent material and outer packaging.
Common buying mistakes
| Mistake | Why it matters | Better approach |
|---|---|---|
| Assuming a specimen bag is the complete system | A bag is usually only the secondary packaging layer | Think in terms of primary, secondary, absorbent and outer packaging |
| Choosing road packaging for air transport | Air transport may involve IATA / PI650 requirements | Check the route and carrier before selecting bags |
| Forgetting absorbent material | Liquid samples require absorbent material between layers | Match absorbent capacity to the sample volume |
| Using a standard bag where 95kPa secondary packaging is required | Standard biohazard or urgent bags may not provide 95kPa performance | Use a 95kPa specimen bag unless the required performance is provided elsewhere in the system |
| Treating temperature control as separate | Temperature-sensitive samples need suitable outer transport planning | Consider insulated medical carriers where appropriate |
| Not checking the completed package | P650 applies to the packaging system, not just individual components | Review how all components work together |
Buyer checklist: choosing UN3373 packaging components
| Question | Why it matters |
|---|---|
| Is the sample liquid, solid or potentially liquid? | Determines whether leakproof packaging and absorbent material are needed |
| What primary receptacle is being used? | The first layer must be suitable for the sample |
| Does the primary receptacle meet the 95 kPa requirement? | If not, the secondary packaging may need to provide this performance |
| Is a 95kPa specimen bag required? | Common requirement for liquid sample transport systems |
| How many primary receptacles are being packed together? | Affects separation, absorbency and bag size |
| Is the movement by road, air or both? | Helps determine whether ADR or IATA bag options are required |
| Is temperature-controlled transport required? | May make an insulated medical carrier appropriate |
| What markings or carrier rules apply? | Helps avoid dispatch issues and carrier rejection |
A better buying question
For many healthcare and laboratory buyers, the question is not simply “which UN3373 bag do I need?” A better question is: which combination of primary receptacle, secondary packaging, absorbent material and outer packaging is suitable for this sample and this route?
Official guidance and buyer responsibility
This guide is intended to help buyers understand the role of different packaging components within a UN3373 Category B sample transport system.
For full and current requirements, buyers should refer to official guidance and transport regulations, including GOV.UK guidance for road transport of UN3373 patient samples, ADR Packing Instruction P650, IATA Packing Instruction 650 / PI650 for air transport, and carrier-specific guidance from the courier, airline or logistics provider being used.
Classification and final packaging selection remain the responsibility of the consignor. Carrier requirements should also be checked before dispatch, especially where samples may travel by air or form part of a wider healthcare logistics network.
View UN3373 specimen bags and medical sample transport products
Universeal supplies a range of products for medical, clinical and laboratory sample transport workflows.
| Product type | Typical role | Link |
|---|---|---|
| 95kPa ADR specimen bags | Secondary packaging for road transport applications | View ADR specimen bags |
| 95kPa IATA specimen bags | Secondary packaging for air transport applications | View IATA specimen bags |
| Standard biohazard specimen bags | Routine sample handling, document separation and workflows where 95kPa secondary packaging is not required or is provided elsewhere | View biohazard bags |
| Urgent sample specimen bags | Priority sample identification and routine specimen handling workflows | View urgent sample bags |
| Absorbent pads | Liquid containment support between primary and secondary packaging | View absorbent pads |
| Insulated medical carriers | Outer transport layer for temperature-controlled sample movement | View medical carriers |
Need help choosing suitable components?
View our UN3373 packaging range or contact our team for help choosing suitable specimen transport bags, absorbent pads and insulated medical carriers for your sample transport route.
FAQs
What is a 95kPa specimen bag?
A 95kPa specimen bag is a secondary packaging bag or pouch designed to withstand an internal pressure of 95 kPa without leakage. These bags are commonly used as the secondary packaging layer within UN3373 Category B sample transport systems, particularly where liquid samples are involved.
Do UN3373 samples always need 95kPa bags?
Not always. For liquid substances under P650, either the primary receptacle or the secondary packaging must be capable of withstanding 95 kPa without leakage. If the primary receptacle already meets this requirement, a 95kPa bag may not be the only possible route. In practice, many buyers choose 95kPa specimen transport bags because they provide a clear secondary packaging option within the wider system.
Are standard biohazard bags suitable for UN3373 samples?
Standard biohazard specimen bags can be useful for routine sample handling, document separation and visual identification, but they should not be treated as a direct substitute for 95kPa specimen transport bags where 95kPa secondary packaging is required. They may be appropriate where the required pressure performance is provided by the primary receptacle, or where the sample has been assessed as an exempt specimen and packaged accordingly.
Are urgent sample bags 95kPa bags?
Urgent sample bags are typically used for priority sample identification and routine specimen handling workflows. Unless specifically tested and supplied as 95kPa secondary packaging, they should not be assumed to provide 95kPa performance. Buyers should check the sample classification, primary receptacle performance and transport route before selecting the appropriate bag.
Are specimen transport bags the same as secondary packaging?
In many UN3373 packaging systems, yes. A specimen transport bag or pouch is commonly used as the secondary packaging layer around the primary receptacle. However, it is only one part of the full packaging system.
Do I need absorbent pads with UN3373 specimen bags?
For liquid samples, absorbent material is required between the primary receptacle and the secondary packaging. The absorbent material should be sufficient to absorb the contents of the primary receptacle or receptacles being transported.
What is the difference between ADR and IATA specimen transport bags?
ADR relates to road transport, while IATA relates to air transport. If samples may be transported by air, buyers should check whether IATA PI650 applies and choose suitable air transport specimen bags.
Can an insulated medical carrier be used as outer packaging?
An insulated medical carrier can provide a practical outer packaging option where medical samples need protection during handling and temperature-controlled transport. It should be used as part of a complete packaging system that also includes suitable primary receptacles, secondary packaging and absorbent material where required. For air transport, buyers should also check IATA and carrier requirements for the outer packaging.
What packaging is needed for Biological Substance, Category B?
Biological Substance, Category B shipments under UN3373 are generally based on a triple packaging system: primary receptacle, secondary packaging and outer packaging. For liquid samples, absorbent material is also used between the primary receptacle and secondary packaging.