Security seals can be split into two main groups: single use and reusable. Single use seals are typically made of plastic or metal, and the used material and production technology is the key to their security level. Reusable seals are usually electronic or mechanical rather than just made from plastic, and if purely plastic, only one part is reusable. Electronic and mechanical seals are generally used for the transportation industry, with seal fixed to the back of trucks, trailers and shipping containers..
A measure of a seal's security is whether it has obtained an ISO PAS 17712 rating. US Customs-Trade Partnership Against Terrorism (C-TPAT) and the World Customs Organisation’s Framework of standards, endorsed and encouraged the use of ISO compliant seals.
The requirements for certain security level of seals are defined in the ISO PAS 17712. The seals that belong to the High security level and Security level are also called "barrier seals". They are made of different metals or metal alloys, meaning that they require special tools to be opened, such as bolt cutters or pliers. Cable seals and bolt seals also fall into this category. Designed to deter opportunistic theft of high value goods, they also can often be branded and numbered to improve tamper resistance and provide excellent security for containers. The seals that are in the Indicative level as to ISO PAS 17712 are made of plastic or thin metal.