The form factor is the physical shape of the SIM. It decides how the SIM survives in the field and how you provision it. Most IoT mistakes here come from treating an industrial device like a phone.
The options
- 2FF / 3FF / 4FF. Removable cards (mini, micro, nano). Cheap and familiar, but the slot is a point of failure under heat, shock and vibration.
- MFF2. A solderable chip rated for harsh environments and a 10+ year life. The default for industrial IoT.
- eSIM (eUICC). A reprogrammable secure element whose operator profile can be changed over the air. Usually delivered as MFF2.
- SoftSIM. No chip at all; the SIM runs in the modem or secure enclave. Saves cost and board space where the modem supports it.
Heads up
If your device ships sealed or lives somewhere you cannot revisit, do not use a removable card. Choose MFF2 or SoftSIM so connectivity can be re-provisioned remotely.