Flexitank and ISO tank basics
Flexitank shipping moves bulk liquids in a large, single-use flexible tank fitted inside a standard 20-foot dry container. One container typically carries about 16,000 to 24,000 liters, depending on the cargo's density and weight limits. Because the cargo travels in an ordinary container, it can use regular container ship services, rail and trucks, and reach inland points that bulk vessels cannot. Flexitanks are used for non-hazardous liquids such as edible oils, glycerin, wine, latex and base oils.
Flexitanks carry bulk non-hazardous liquids, such as edible and vegetable oils, glycerin, wine, juice concentrates, syrups and food ingredients, latex, lubricants and base oils, non-hazardous liquid fertilizers and non-hazardous chemicals. ISO tanks carry both non-hazardous and hazardous liquids, including products that need a reusable steel tank, heating or a dangerous goods classification. The right choice depends on the product's safety data sheet, the volume, the route and the receiver's equipment, so share these details when you request a quote.
For non-hazardous liquids moving in container-sized lots, a flexitank in a 20-foot container is often the most economical choice, because it is single-use and needs no cleaning or return. ISO tanks are reusable steel tanks suited to hazardous cargo, sensitive products and cargo that needs heating or tight hygiene control. Bulk vessels, such as parcel tankers, suit large single lots of thousands of tonnes moving between terminals with tank storage. Many shippers use more than one option, and a bulk liquid logistics provider can compare flexitank and ISO tank options for a given lane.
Yes. Many hazardous liquids move in ISO tanks, while flexitanks are not used for dangerous goods. Hazardous cargo by sea is governed by the IMDG Code, which sets requirements for classification, the type of portable tank permitted, filling, marking and documentation. The shipper provides the safety data sheet and a dangerous goods declaration, and the carrier must accept the booking. The tank itself must be suitable for the specific product.
A flexitank in a 20-foot container typically holds about 16,000 to 24,000 liters (16 to 24 m³). The practical limit is often weight rather than volume: multiply the volume by the cargo's density and check the result against the container payload and the road and rail weight limits on each leg. Denser cargoes use smaller flexitanks, and lighter liquids can use larger ones. Filling close to the flexitank's rated capacity is generally recommended to limit surge. ISO tank capacities and fill limits vary by tank and cargo, so confirm the right fill for your product and route.
The door-to-door process
A typical door-to-door move follows these steps. (1) The shipper shares the product, volume, origin, destination and timing. (2) Equipment and vessel space are booked with a carrier that accepts flexitank cargo. (3) A container is inspected and prepared, and the flexitank and bulkhead are fitted. (4) The cargo is loaded at origin. (5) The container moves by truck or rail to the port. (6) Export documents are filed. (7) Ocean transit. (8) Import clearance at destination. (9) Delivery and discharge at the receiver. A door-to-door provider coordinates each of these steps.
Transit time depends on the trade lane, the carrier's schedule, any transshipment and the inland legs. As a general guide, port-to-port ocean transit ranges from under two weeks on shorter direct routes to six weeks or more on long or transshipped routes. Add time for container preparation and loading at origin, trucking or rail to the port, customs clearance and delivery to the receiver. Port congestion and seasonal demand can add delays. Ask for routing and schedule options for your specific shipment when you request a quote.
At origin, a suitable 20-foot dry container is inspected and prepared. The flexitank is laid out with its valve at the door end, any heater pad is placed on the floor beneath it, and the bulkhead is installed. The loading hose is connected to the valve, and cargo is pumped in from a tank truck, rail car or storage tank at a controlled rate. Loading stops at the agreed volume, the valve is secured, and the container is labeled and sealed. The loaded quantity is recorded for the documents. Tank fitting and container preparation are coordinated with the loading site in advance.
The receiver checks the container and bulkhead before opening the doors. Cargoes that thicken in cool weather, such as some oils, fats and glycerin, are warmed first using a heater pad placed under the flexitank before loading; the receiver connects a heat source and allows time for the cargo to warm. The discharge hose is then connected to the valve, and the liquid is pumped out or drained by gravity. The empty flexitank is removed and the container returned. Confirm the receiver's pumps, fittings and heating needs before the shipment leaves origin.
Transloading moves liquid from one mode of transport to another on the way to the port. In a common pattern, cargo arrives by rail tank car at a transload facility, where it is pumped directly into flexitanks fitted in 20-foot containers. The containers then move to the port by truck or rail for ocean shipment. This lets producers that ship by rail reach export markets without loading containers at their own plant. Timing, volume per rail car and the facility's capabilities need careful planning, which is why these multimodal moves are usually arranged by a bulk liquid logistics provider.
Container preparation and tank fitting are usually arranged by the forwarder or flexitank provider, at the loading site or a nearby depot. The work includes selecting and inspecting a suitable container, cleaning it, lining it where required, laying out the flexitank, placing heater pads if needed and installing the bulkhead. Problems in transit are often linked to container condition or fitting, so this step deserves care. Ask whether tank fitting and container preparation are included when you request a quote.
Carriers, documents and insurance
Many container lines accept flexitank cargo, but each sets its own rules. These can cover approved flexitank suppliers, required liability insurance, evidence of testing, container standards, permitted cargoes and routes, and booking procedures. Many lines refer to industry guidance such as the Container Owners Association (COA) code of practice for flexitanks. Acceptance can vary by trade lane, and some routes or ports may not accept flexitanks at all. A specialist forwarder checks acceptance before booking.
Common documents include the bill of lading (BL), commercial invoice, packing list, safety data sheet (SDS, formerly called MSDS) and a Certificate of Analysis (COA) for the cargo. Depending on the product and destination, you may also need a certificate of origin, phytosanitary or health certificates for food products, and import permits. Hazardous cargo in ISO tanks also needs a dangerous goods declaration. For US exports, Electronic Export Information is filed in AES where required. Your forwarder coordinates shipping documentation with the shipper and receiver.
At origin, export declarations are filed and the cargo must match its documents. At destination, the importer or its customs broker files the import entry, pays duties and taxes, and meets any product-specific rules, such as food safety requirements, chemical registration or sampling. Liquids are classified precisely by tariff code, so accurate product descriptions and Certificate of Analysis data help avoid delays. Rules differ by country, so check them before shipping. On a door-to-door shipment, the provider coordinates the handoffs with customs brokers at origin and destination.
Two kinds of cover are commonly involved. Cargo insurance protects the value of the liquid against loss or damage in transit, which can include leakage, depending on the policy terms. Separately, container lines often require flexitank liability insurance from the flexitank provider, covering damage to the container, other cargo or third parties if a flexitank fails. Review policy limits, exclusions and contamination cover before shipping, and ask your forwarder what is in place for a given booking.
Costs, trade lanes and tracking
The main cost drivers are the ocean freight rate on the lane, the flexitank and its fitting, container preparation, trucking or rail to and from the ports, and terminal and documentation charges. Destination costs include import clearance, delivery and discharge, plus heating if required. Weight limits decide how much cargo each container can carry, which drives the cost per liter. Market rates, fuel surcharges and seasonal demand change over time. Compare the total door-to-door cost per liter, not only the ocean freight, and ask for a door-to-door quote on your specific lane.
An ISO tank can be the better choice when the cargo is hazardous, needs controlled heating, is dense enough that a flexitank cannot be filled efficiently within weight limits, or must meet strict cleanliness requirements. ISO tank costs include tank rental, cleaning and repositioning, but the tank is reused. For a non-hazardous cargo shipped in full-container volumes, a flexitank is often cheaper because it is single-use and has no return leg. The answer depends on the product and lane; a provider that handles both flexitanks and ISO tanks can compare the options.
Flexitanks and ISO tanks move bulk liquids on most major container trade lanes. From the United States, examples include exports of oils, chemicals and other liquids to Asia, Latin America and Europe, as well as imports of edible oils, wine and concentrates. Producers in Asia and Latin America also ship bulk liquids to other regions. Carrier acceptance of flexitanks can vary by lane and port, so check routing early.
Container shipments are usually tracked through carrier milestones, such as gate-in at the port, loading on the vessel, transshipment, discharge and gate-out, linked to the container and BL numbers. For door-to-door moves, the inland legs, documentation and customs status matter as well. Some forwarders bring this information together in software, so shippers can see status, documents and exceptions in one place rather than across several carrier websites. Ask a prospective provider whether it offers this kind of supply-chain visibility.
Choosing a provider and getting a quote
A bulk liquid logistics specialist arranges door-to-door ocean shipping, primarily of bulk non-hazardous liquids in flexitanks and of non-hazardous and hazardous liquids in ISO tanks. Services can include multimodal moves, such as rail to transload into flexitanks followed by ocean shipping, as well as tank fitting, container preparation and supply-chain software visibility. Because the work centers on bulk liquids, a specialist can answer flexitank and ISO tank questions directly.
For bulk liquids in flexitanks or ISO tanks, a bulk liquid specialist focuses on what those shipments need: door-to-door ocean shipping, multimodal moves, tank fitting, container preparation and visibility. For dry or packaged cargo, a general cargo forwarder is usually the better fit. If you ship both, match the provider to the cargo.
A complete quote request includes the product name and its safety data sheet; whether it is classified as hazardous; its density and any heating needs; the volume per shipment and expected frequency; the origin address and how the cargo arrives there (tank truck, rail car or storage tank); the destination address and the receiver's discharge equipment; target dates; and any documents or certificates the receiver requires. The more complete the details, the more accurate the routing and pricing will be.
Contact a flexitank or ISO tank logistics provider with your product, volume, origin, destination and timing. The provider reviews the cargo and route, checks equipment and carrier options, and replies with a door-to-door proposal for flexitank or ISO tank shipping. If you are not sure which option fits, describe the cargo and ask for advice. Including the safety data sheet and the product's density from the start helps avoid back-and-forth and speeds up the quote.