Flexitanks Versus ISO Tank Containers for Bulk Liquid Transportation

Flexi-Tanks and tank containers are both used to transport bulk liquids. Depending on what you’re shipping, from where, and to where you’re cargo is going, one method might be better than the other. Bulk liquid transportation is an important segment of the freight transportation industry. Depending on the type of product being shipped, the origin of the product and the cargo’s destination, the most reliable and economical method of bulk liquid transportation may not be obvious.  While ISO tank containers and flexitanks are both used to efficiently transport bulk liquids, there are some distinct differences between these two options.

What is an ISO Tank Container?

An ISO tank container is a stainless steel tank surrounded by various protective layers which can transport both hazardous and non-hazardous bulk liquids by sea, railway, or roads. ISO tank containers are built to the ISO standard (International Organization for Standardization). The typical design has a manhole on the top along with at least one valve and another valve on the bottom. Bulk liquid ISO tanks are easily distinguished by their cylindrical shape and may be lined to minimize wear and corrosion from the contents, but they lack the large disposable bladder lining common in flexitanks. In addition to transporting bulk liquid gas and fuel, they can also be built specifically for food transport.

Liquids Transported by ISO Tank Containers

Food Grade Liquids

·      Milk and other dairy

·      Juices

·      Alcohol

·      Liquefied sugars

·      Molasses

·      Vegetable oils

Non-Edible Liquids

·      Gasoline

·      Diesel

·      Heating oil

·      Industrial chemicals

·      Liquefied petroleum gas


Depending on their contents, ISO tank containers may be pressurized, insulated, or refrigerated to protect the cargo.

Size of ISO Tank Containers
Tank containers, trailers, and chassis come in several models, but they all transport tank containers with the ability to carry between 5,500 and 11,600 gallons (approximately 20,800 to 42,900 liters) with respect to weight restrictions. Smaller equipment may be used for local deliveries and carry less than 3,000 gallons.

Benefits of ISO Tank Containers
An advantage of tank containers over flexitanks is that tank containers may have up to six (6) compartments.These extra compartments makes them ideal for transporting petroleum products because multiple grades can be transported in one trip. There’s also a wide variety of delivery options available with tank trailers and chassis, because the same product for delivery to various customers’ may be aggregated. Tank containers are more durable and have a lifespan of approximately 30 years compared to flexitanks which are typically disposed of after carrying a liquid.

Most ISO Tank containers are made of marine grade stainless steel inner shells with high corrosion resistance. This steel shell provides maximum protects of the cargo so that it is delivered safely and is free of contaminants. Stainless steel tank containers are carefully designed and rarely leak, which significantly reduces the risk of spillage during transportation and loading/discharging processes.

In addition, all ISO tank containers’ valves are required to be inspected by a competent individual prior to loading in order to promote safety and compliance.

Sanitation of ISO Tank Containers
Before an ISO tank container is reused, it must be thoroughly cleaned and certified. This often costs the recipient of a shipment a few hundred dollars. There are stringent sanitation procedures for food grade tanks depending on what food is being transported and for cleaning of chemical transport tanks. Tank containers are typically designated for a particular product be it foodstuffs or chemicals and tanks once used for chemicals, may never be used for edible products.

What are FlexiBags and Flexitanks?

A flexibag is a hermetic sealed, collapsible and flexible bag/bladder that when full fits inside a standard 20-foot intermodal container, making it a flexitank. These two terms are often used interchangeably. They’re typically used to transport food grade liquids, but they may also be used to transport non-edible liquids.

Liquids Transported by Flexitanks

Food Grade Liquids

·      Oils and fats

·      Juice and juice concentrates

·      Wine and water

·      Syrups

·      Food additives

·      Pharmaceuticals

Non-Edible Liquids

·      Industrial oils

·      Cleaning liquids

·      Emulsions

·      Fertilizers

·      Latex and waxes

·      Ink

To prevent certain liquids from thickening during transport, heat pads can be added to the tank. Refrigeration is also available to prevent milk, wine, or other products from spoiling during transportation.

Size of Flexitanks
Flexitanks come in a variety of sizes with standard volumes ranging from 16 to 24 thousand liters. Small volumes, some as low as 10,000 liters, are also available.

Benefits of Flexitanks
Depending on the size of your shipment, using flexitanks can save you money, because the flexibags (the bladders inside the flexitanks) expand to fill the intermodal container. In addition, loading and unloading can readily be completed by releasing the liquid from one vessel to another. Therefore, this process will reduce loading / unloading time, and minimize the potential for cargo loss during the loading and unloading process.

Sanitation Standards of Flexitanks
Food grade Flexitanks have to meet strict sanitation standards. The bladders are typically for one-time-use only. Despite having to purchase new Flexitanks for each shipment, there may still be a net savings due to the advantages of Flexitanks outline above.

Flexitanks vs. ISO Tank Containers

While both ISO tank containers and flexitanks possess unique advantage depending on your cargo and shipping requirements, ISO tank containers are the industry preferred method of transporting bulk liquid. Tank containers and are favored based on their quality, durability, safety, and versatility.

If you’re looking for ways to reduce bulk liquid shipping costs, contact us today to discuss your needs.


April Uhlenburg
April U

April has been working with Penn Intermodal’s Sales and Operations teams to educate clients on the benefits of leasing chassis for bulk liquid storage and transport since 2012.