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What is an MFF2 SIM?
MFF2 (Machine Form Factor 2) refers to a specific physical format of an embedded SIM. Instead of a removable card, the SIM is soldered directly onto the device’s PCB during manufacturing. It becomes a permanent part of the hardware, with no tray, no slot, and no physical access once deployed.
It’s often described as an “eSIM,” but that’s not quite right. MFF2 defines the form factor – whereas eUICC (often called eSIM) defines the capability to manage profiles remotely. The current trend is that modern MFF2 SIMs support eUICC, but the two are not the same thing.
In practice, MFF2 is the standard form factor for IoT devices that need to operate reliably over long periods without human intervention.
Why MFF2 is used in IoT
Embedded SIMs such as MFF2 solve a set of very practical problems that removable SIM cards were never designed for. IoT devices are often sealed, deployed in difficult environments, and expected to run for years without maintenance.
By removing the physical SIM interface entirely, embedded SIMs improve durability and reduces failure points. There are no connectors to wear out, no risk of SIM removal, and no need to access the device after deployment. This is critical in environments like industrial equipment, vehicles, or outdoor infrastructure.
It also simplifies manufacturing. The SIM is integrated during production, so devices leave the factory fully assembled and ready for connectivity. There is no manual SIM insertion step, which reduces complexity and improves consistency at scale.
Over time, this becomes a lifecycle decision as much as a hardware one. If a device is expected to operate for 5–15 years, the SIM needs to be as reliable as the rest of the system.
Comparing embedded SIM form factors: MFF2 vs MFF-XS vs iSIM vs SoftSIM
MFF2 sits in the middle of an evolving hardware landscape. Newer form factors and approaches are emerging, but they each come with trade-offs.
MFF-XS
MFF-XS follows the same principle as MFF2, but in a smaller package. It’s designed for highly space-constrained devices, such as wearables or compact sensors. In theory, it offers the same capabilities in a reduced footprint. In practice, adoption is still limited. The ecosystem is less mature, and most modules and manufacturers continue to standardize around other form factors.
iSIM
iSIM takes a different approach. Instead of requiring a separate SIM component, iSIM integrates SIM functionality directly into the device’s main system-on-chip (SoC). This reduces board space and can improve power efficiency by removing the need for a discrete SIM chip.
However, this level of integration introduces new dependencies. Because the SIM functionality is tied directly to the chipset, the SIM lifecycle becomes closely linked to the chipset vendor. This can limit flexibility when managing connectivity providers or updating provisioning models over time. For deployments operating across multiple regions and networks, that tighter coupling can become a consideration.
SoftSIM
SoftSIM takes integration even further by implementing SIM functionality entirely in software rather than in a dedicated hardware element.
In this model, device identity and authentication are handled by secure software running on the device.This approach offers advantages in terms of hardware simplicity and manufacturing flexibility, since no physical SIM component is required.
Learn more about the Onomondo SoftSIM
Where MFF2 fits today
Among these options, MFF2 represents a well-established embedded SIM form factor with broad industry support. It works across many existing cellular modules and manufacturing workflows, making it a practical option for device manufacturers looking to integrate connectivity directly into their hardware.
While interest in newer approaches such as MFF-XS, iSIM, and SoftSIM continues to grow, MFF2 remains a familiar and widely supported choice for teams designing connected devices today.
How connectivity works on MFF2 sims
The form factor defines how the SIM is installed, but not how connectivity is managed. That depends on the SIM architecture.
Multi-IMSI
Multi-IMSI (Multiple International Mobile Subscriber Identities) SIMs store multiple network identities on the SIM. The device switches between them based on location or predefined rules. This provides some level of resilience, but it is inherently limited. The available networks are fixed at the time of provisioning, and adding new ones later is difficult.
eUICC
eUICC (embedded Universal Integrated Circuit Card) introduces remote provisioning. Instead of preloading all network profiles, the SIM can download and switch profiles over the air. This improves flexibility, especially for global deployments, but it also introduces operational overhead. Profiles need to be managed, distributed, and maintained over time.
A note on eUICC: Until recently, remote SIM provisioning with eUICC for IoT was complex. The GSMA SGP.22 eSIM standard designed for consumer devices was limited for OTA profile updates in network- and location-constrained devices in bulk. With the introduction of SGP.32, the eSIM IoT specification, these issues are resolved and eUICC becomes more accessible for IoT fleets.
Single global profile (cloud-managed connectivity)
Some connectivity providers (including Onomondo) take a different approach by keeping the SIM architecture simple and moving the intelligence into the network platform.
With this model, the SIM uses a single global identity rather than multiple IMSIs or downloadable profiles. Devices attach to available local networks, while routing, network selection, and connectivity management are handled in the cloud.
This reduces the need for IMSI switching or profile lifecycle management on the SIM itself. Instead, connectivity decisions are controlled centrally through the platform.
