What is a SIM form factor?

SIM cards today come in various sizes or form factors. When the first SIM cards appeared in the 1980s, there was only one form factor: the credit-card-size 1FF. Today, there are four standard sizes of removable SIMs, along with the embedded SIM (MFF2). As mobile phones shrank over the years, so did their SIM cards.

Today’s IoT devices typically use machine-to-machine (M2M) SIMs, either in the form of removable cards or embedded chips. M2M SIMs are designed for sending and receiving data (instead of voice calls and text messaging), include more memory than traditional SIMs, and are designed to last longer.

Choosing the best SIM for your device

Form factor is just one element of choosing the right SIM for your IoT (internet of things) device. The best decision depends mainly on the size of the device and how much space can be allotted to the SIM card. It’s important to note that the chips themselves are the same on form factors 2FF–4FF—the difference is in the size and thickness of the surrounding card.

SIM card form factors for IoT

• Mini SIM (2FF)
• Micro SIM (3FF)
• Nano SIM (4FF)
• Embedded SIM (MFF2/DFN8)

Mini SIM (2FF)

At 25mm x 15mm x 0.71mm, the Mini SIM is the largest removable SIM card currently in use. It’s been around since the mid-1990s, when it emerged as a smaller option (at the time) for shrinking mobile devices. Today, the Mini SIM still works well for larger connected devices, like cars and vending machines.

Micro SIM (3FF)

The Micro SIM measures 15mm x 12mm x 0.71mm, significantly smaller than the Mini SIM. It’s large enough to be manageable for easy physical swapping of SIM cards, but it fits better in mid-size IoT devices like tablets and telehealth monitors.

Nano SIM (4FF)

Measuring at 12mm x 8.8mm x 0.71mm, the Nano SIM is both smaller and slimmer than its counterparts. It’s an ideal solution for compact IoT devices including wearable technology and mobile payment equipment.

Embedded SIM (MFF2/DFN8)

The embedded SIM or eSIM is soldered directly to the device’s motherboard, so it’s fully encased in the device. That means it’s a great choice for IoT devices deployed outdoors or in harsh conditions. For large-scale deployments, choosing an eSIM can also simplify your supply chain because it removes the step of physically installing a SIM in every device. There’s often confusion around the term eSIM, as many people use it to refer to eUICC-enabled eSIMs. But the eSIM itself is simply what it claims to be—an embedded SIM—and does not automatically enable remote provisioning. More IoT designers are starting to embrace eUICC-enabled eSIMs, though, because of their versatility and flexibility. (For more on that, check out our eUICC SIM platform, Hologram Hyper.)

Factors to consider

When matching your device with the perfect SIM form factor, size and accessibility are the main concerns. Larger devices can accommodate the bigger SIM form factors, while smaller devices demand the tinier ones. Beyond those basics, here are a few other considerations to keep in mind:

Protective casing differences

While its slenderness is an advantage for some applications, it also means the Nano SIM lacks the protective layer of plastic around the contact chip that the other removable form factors have. For that reason, the Nano SIM might not be the best sim technology for IoT devices that are exposed to extreme temperatures or weather conditions. For devices deployed outside, underground, or in otherwise damaging environments, the eSIM provides an ideal solution since it’s sealed within the device.

Security concerns

Depending on the location and circumstances of the deployment, some IoT devices will be at higher risk of security breaches than others. Removable SIM cards have historically been a point of vulnerability as bad actors can take one from a device like a scooter, and attempt to use it on a phone or tablet to connect to the Internet. IoT SIMs equipped with multi-factor authentication guard against security breaches by using key rotation, signing, and message authentication codes to verify an IoT device’s identity and secure its communications. These security safeguards stop hackers from ripping the SIM to stream Netflix or scroll social media. And some IoT platforms, such as the Hologram Dashboard, allow you to trace the location of SIMs, matching them against the device’s International Mobile Equipment Identity (IMEI) and notifying you with an alert if the SIM turns up in a different location than the IMEI. When you choose a SIM for your device, look for security features such as these to offset potential risks.

Remote provisioning abilities

As IoT deployments expand around the world, more organizations are looking for remote provisioning abilities in their SIMs to allow more efficient and flexible connectivity. eUICC-enabled removable SIMs and eSIMs can both provide this capability, allowing operators to swap out subscriber profiles over the air (OTA) using a method called Remote SIM Provisioning (RSP). Whether or not you need RSP is a question to pursue with your design team, but there are several benefits of building with eUICC—for example, it enables a single SKU to work for multiple deployments around the world and gives you the ability to update SIM profiles after devices are deployed. If your deployment is large, these advantages could yield significant savings in effort and costs.

No matter which SIM form factor you choose for your device, you’ll want to make sure it can provide the longevity, durability, and global connectivity you need for your deployment. Hologram makes IoT SIM cards in all form factors, including the eSIM (MFF2). Our hardware-agnostic global SIM card or chip allows you to connect to every network in every country and automatically switch carriers to ensure your device has the best available service (2G, 3G, 4G LTE, and CAT-M1), wherever it may be.

On the management side, you can keep track of your devices using either the Hologram Dashboard, which provides simple collaborative management tools to oversee device health, IoT connectivity, and security, or through our modern REST API.