InTek Logistics Blog

Securing cargo: Container seals explained

Written by Kevin Baxter | Aug 21, 2025

They range from simple to complex with different materials and designs, but one thing they share is a purpose: to secure cargo (or demonstrate cargo security). What are they? Container seals, which essentially serve as locks or markers to prevent - or at the very least deter - cargo theft or unauthorized container access. While variety is the spice of life, not every security seal is right for every situation. So let's rundown the options to keep your products protected from cargo theft. 

What are container seals?

Container seals are exactly what the name implies, small, locking devices used to secure cargo within a container - or at least show if a container has been tampered with. They tend to be temporary in nature, as once containers reach their destination, many types of these security seals are destroyed during removal (since they must be cut off). However, some seals are designed for multiple uses. Carriers do require seals of some type to move containers, with the requirements varying by product, transport method, lane, etc.

Types of container seals

There are many types of container seals for shippers to choose from. But all those options are broken into two main categories: indicative or preventative. Indicative seals are there to indicate whether a container has been tampered with, as they provide minimal security in and of themselves. Preventative seals on the other hand, function more as locks to prevent a breach.

Within the preventative seal designation are both security seals and high-security seals. Security seals provide some level of protection (requiring basic tools to remove), while high-security seals can only be removed with specialized equipment and/or extensive effort. In some cases, indicative and preventative seals are used in tandem. And keep in mind, each seal is numbered and sometimes branded as an added tracking mechanism. These may feature QR codes or barcodes as well.

Plastic seals

Falling firmly into the indicative category, plastic seals are widely used as a budget-friendly solution. Best suited for short-term applications where visual evidence of tampering is all that’s needed, these seals offer versatility for a variety of situations. But keep in mind, they’re quite simple to bypass if security is a priority. 

Tin seals

Tin seals are also indicative and provide only slightly more security than their plastic counterparts. These are again used more to show tampering than prevent entry.

Cable seals

A cable seal is a tough, flexible cable (typically made of steel) designed to thread through a container door’s locking mechanism and then secure with a durable tamper-evident lock that could be made of metal, plastic or a combination of the two. Cable seals act as indicators and provide some security, though many types are easier to break than some stronger seals.

Bolt seals/Bullet seals

Bullet seals are cylindrical and look like - you guessed it - a bullet. Also known as bolt seals (especially the ones that look less bullet-like), they’re engineered to fit securely through the locking mechanisms of shipping containers, trailers, or cargo doors - creating a tough seal that makes tampering a real challenge for would-be thieves. 

Barrier seals

Barrier seals stand at the top of the security game for container shipping. These heavy-duty devices are installed on the locking rods of shipping container doors, locking both doors together for maximum protection. They're typically easy to install without the need for special tools, but especially difficult to take off without them. Most are built for single-use, as they are destroyed upon removal. 

Hasp locks

Hasp locks are special locks placed on hasps (hinged fastening plates) of container doors. This padlock is made of a reinforced steel designed to withstand bolt cutters and other tampering - clearly landing in the preventative category.

Electronic seals

A variety of seal types may also feature some type of electronic technology. Electronic seals (or electronic locks) may have RFID chips, GPS trackers, climate monitoring and other tech that can indicate when a seal has been broken - providing shippers and carriers added visibility into the journey of each container.

A few notes about seals: no seal is unbreakable, but some are much tougher to crack than others. Indicative seals can be breached with a strong grip, while the best high-security seals require specialized equipment. There are variations within this list of seals as well, and some features - like RFID - aren't limited to electronic seals for instance.

ISO PAS 17712:2013 high security seal standards 

When moving high-value loads, shippers need not guess which seals to use thanks to the ISO/PAS 17712:2013 high security seal standards. The ISO (International Standards Organization - which you may be familiar with when it comes to ocean containers) developed these PAS (Publicly Available Specifications) specifically for Freight containers – Mechanical seals – Classification and performance.”

These are guidelines specifically meant to categorize container seals as indicative, security or high-security. The focus is on what clears the bar for high security though, and to that end there are particular requirements for how seals are constructed and tested to stop thieves from breaching them - as well as how well they show evidence of tampering so that carriers and shippers can tell if unauthorized access has occurred. 

To meet this standard requires independent confirmation via three steps:

  • Tests to determine a seal's physical strength
  • Audits of the seal manufacturer's security practices
  • Demonstrable, tell-tale indications of tampering

The outcome of the testing determines whether seals are placed into the high-security, or 'H' category, which may be required to move high-value products and is required by U.S. Customs and Border Protection's C-TPAT (Customs-Trade Partnership Against Terrorism) program.

Shipping cargo securely

Using a seal alone is far from the only method to get added visibility and security, as containers themselves can be equipped with temperature monitoring, GPS tracking and door sensors among other features. In fact, seals should be part of a holistic approach to securing cargo with other tips including keeping high-value cargo unmarked, loading it deeper within a container and coordinating with freight providers, railroads, and any other carriers you may use.

Working with a logistics provider who values security is a key factor as well, and at InTek Logistics, we help ensure you'll have the right measures in place for each shipment. Start your journey with us today by requesting a quote. For more information about InTek Intermodal, or the logistics and supply chain space in general, check out our Freight Guides.