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How to pack UN 3373 and Category A infectious substances: triple packaging guide

Biological substances (UN 3373, Category B) and infectious substances (UN 2814 / UN 2900, Category A) always travel in triple packaging: a leakproof primary receptacle, a leakproof secondary packaging and a rigid outer packaging. Liquids add absorbent material and resistance to 95 kPa; Category A also needs UN-certified «CLASS 6.2» packaging.

✓ Reviewed by an ADR Dangerous Goods Safety Adviser · Updated: 04/10/2026

The six layers of a dry-ice shipment of biological samples

The layers, in the order you pack them

  1. Primary receptacle (mandatory): the tube or vial, leakproof. For liquids, absorbent material around it — enough to soak up the entire contents.
  2. Secondary packaging (mandatory): leakproof — usually a 95 kPa bag. The primary or the secondary must withstand a 95 kPa pressure differential.
  3. Rigid container (extra): a plastic cylinder adds protection; the regulations ask for at least three components, so more is allowed.
  4. Outer packaging (mandatory): rigid, with at least one face of 100 × 100 mm. For Category A it is a UN-certified box marked «4G/CLASS 6.2/…», with the itemised list of contents between the secondary and the outer packaging.
  5. Dry ice (extra): around the secondary packaging, never inside it; the packaging must let the CO₂ escape.
  6. Overpack (extra): the insulated transport box. It does not need a UN packaging mark — it is marked «OVERPACK» and repeats the marks and labels that are no longer visible.

The absorbent is not a layer: it goes with the primary receptacle and is only required for liquids.

Category A or Category B?

Category BCategory A
UN numberUN 3373UN 2814 (humans) · UN 2900 (animals only)
Packing instructionP650 (PI 650 by air)P620 (PI 620 by air)
Packagingtriple packaging, 1.2 m drop testUN-certified «CLASS 6.2» packaging
Mark / labelUN 3373 diamond (≥ 50 mm) + «BIOLOGICAL SUBSTANCE, CATEGORY B»class 6.2 hazard label (≥ 100 × 100 mm)
Extra requirements—95 kPa and −40 °C to +55 °C, list of contents

Dry ice and overpack

  • Dry ice (UN 1845) needs the class 9 label and the «UN 1845 Dry ice» mark with the net weight in kg on the package or overpack that contains it.
  • If the dry ice is in the transport box, its labels go on that box — not on the inner 4GV box.
  • The overpack carries «OVERPACK» and repeats the UN 3373 or 6.2 marking, the dry ice labels and shipper/consignee.
  • By air, give the name and telephone number of a responsible person.
Correctly marked Category B and Category A packages

The correct boxes

  1. Category B: UN 3373 diamond of at least 50 mm with «BIOLOGICAL SUBSTANCE, CATEGORY B» next to it, letters of at least 6 mm.
  2. Category B with dry ice: class 9 label + «DRY ICE UN 1845» with the kg.
  3. Category B: shipper, consignee and responsible person with telephone.
  4. Category A: class 6.2 label of at least 100 × 100 mm.
  5. Category A: one marking label with UN 2814, proper shipping name, net quantity, shipper, consignee and responsible person with telephone.
  6. Category A: the UN packaging mark «4G/CLASS 6.2/…» of the certified box.

Products for this shipment

Available at MYDG.SHOP.

Pharma and laboratory label kit — 150 labelsPharma and laboratory label kit — 150 labelsUN 3373 mark with «Biological Substance, Category B»UN 3373 mark with «Biological Substance, Category B»€6,50Class 6.2 infectious substance labelClass 6.2 infectious substance label€6,50Dry ice labels (UN 1845)Dry ice labels (UN 1845)2 productsOverpack labelsOverpack labels3 products95 kPa secondary bags95 kPa secondary bags8 productsAbsorbent padsAbsorbent pads7 productsUN class 6.2 certified packaging (Category A)UN class 6.2 certified packaging (Category A)4 productsDry ice and temperature-controlled shippersDry ice and temperature-controlled shippers26 products

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Frequently asked questions

Is triple packaging mandatory for UN 3373?

Yes. Packing instruction P650 requires at least three components — primary receptacle, secondary packaging and outer packaging, one of the last two rigid — for solids and liquids alike.

Is absorbent material always required?

No. It is required for liquids: enough absorbent between the primary receptacle and the secondary packaging to absorb the entire contents. Solids do not need it.

What is the difference between Category A and Category B?

Category A (UN 2814 / UN 2900) can cause permanent disability or fatal disease on exposure and needs UN-certified «CLASS 6.2» packaging and the 6.2 label. Category B (UN 3373) covers the other infectious substances and uses the UN 3373 diamond with «BIOLOGICAL SUBSTANCE, CATEGORY B».

Where do the dry ice labels go?

On the package or overpack that actually contains the dry ice: class 9 label plus «UN 1845 Dry ice» with the net weight in kg. If the dry ice is in the outer transport box, they go on that box.

Does the overpack need a UN packaging mark?

No. The UN mark goes on the certified packaging inside. The overpack is marked «OVERPACK» and repeats the marks and labels that are no longer visible.

Some airlines ask for Category A packaging for Category B — is that allowed?

Yes, it is a stricter choice, and some carriers require it. Check with the carrier before shipping.

Guidance only. It does not replace the regulations in force: the consignor classifies the goods, decides and signs. MYDG.SHOP SL · Badajoz (Spain).