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.
Heads up
If your device ships sealed or lives somewhere you cannot revisit, do not use a removable card. Choose an MFF2 eSIM so connectivity can be re-provisioned remotely.