An ISO tank is a reusable steel tank in a standard frame, and a flexitank is a single-use plastic bag fitted inside a 20 ft container. Use an ISO tank for dangerous goods, high-purity or temperature-sensitive liquids, and a flexitank only for non-hazardous bulk liquids that suit the bag.
Both let you ship liquid in bulk instead of drums. They differ in cost structure, safety and what they can legally carry.
What can each one carry?
ISO tanks are approved as portable tanks under the dangerous goods rules, and a tank is approved for specific substances through its tank instruction. They can carry many hazardous liquids if the tank type suits the product, and they can be insulated and heated for products that thicken in the cold. Capacities are commonly in the range of 20,000 to 26,000 litres. Tank types differ in design pressure, material and fittings, so the operator should confirm the tank is approved for your UN number before booking.
Flexitanks usually hold roughly 16,000 to 24,000 litres and are made for non-hazardous liquids. They are generally not accepted for dangerous goods, and shipping lines set their own limits on what they will take. Their liners must also be compatible with the liquid.
When should you choose an ISO tank?
- The product is dangerous goods, such as a corrosive or flammable liquid.
- The product is high-purity and cannot risk contamination from a liner.
- The product needs heating or temperature control during the journey.
- You ship the same product on a regular schedule and can plan tank returns.
ISO tanks carry rental, positioning and return logistics. Tank cleaning between loads is vital: see ISO tank shipping and cleaning. Delays in returning the tank can lead to detention charges.
When is a flexitank the right choice?
A flexitank can make sense for non-hazardous, stable liquids in volume, such as certain oils and non-dangerous aqueous products, where nobody has to clean or return a tank. It travels in a normal container and is disposed of after use.
The risks are real. Poor installation or a pinhole can leak into the container, and the liner can interact with sensitive products. Pick a reputable supplier, check the liner compatibility, and see flexitanks for chemicals. The destination also needs a way to unload and dispose of the liner. Check that your receiving site can handle a flexitank discharge, since it needs a pump, a connection and a plan for the empty liner. A buyer with no suitable equipment may find the saving on packaging disappears at the unloading stage.
What should you confirm with the factory?
- The exact product, concentration and any additives, so the carrier can match the tank or liner.
- The freeze point and viscosity at transit temperatures.
- Who loads, who seals, and who takes the sample, with a loading survey if the lot is large. See the loading survey for bulk chemicals.
How we help
We check the tank or liner, the cleaning certificate and the loading. To choose between bulk options for your product, book a free sourcing review.