What is an eSIM and how does a travel eSIM actually work?

An eSIM is a chip soldered into the phone’s mainboard that holds a re-writable cellular identity, instead of a removable plastic SIM card. The identity itself — the IMSI, the keys, the carrier’s profile — is the same data that has always lived on a SIM; what changed is that it now downloads over the internet rather than arriving on a piece of plastic.

A travel eSIM is one specific use of that capability: a third-party reseller (Airalo, Yesim, Holafly, Saily, and the rest of the field on the eSIMBench leaderboard) buys data wholesale from local carriers in dozens of countries, packages it into per-country or regional data-only plans, and sells those plans through their own app. The buyer scans a QR code or taps an install link, the eSIM profile lands on the phone, and the data starts working — usually within a few minutes of arriving in the destination country.

The practical difference between an eSIM and a regular roaming SIM is that nothing has to ship in the mail and no kiosk has to be open. The buyer can install the profile from home before a trip and have working data the moment the plane lands. The practical difference between a travel eSIM and the home carrier’s international roaming is price: a 5 GB regional plan from a travel-eSIM reseller is typically a small fraction of the equivalent roaming charge from a US or UK carrier, because the reseller is buying directly from local networks and skipping the home carrier’s roaming margin.

Travel eSIM plans are data-only. They do not get a phone number that can receive SMS. Two-factor codes still arrive on the home number, because the home SIM is still active on the dual-SIM phone — the travel eSIM is just the data carrier. Voice calls and SMS continue to route through the home carrier’s network (and roam at home-carrier rates), which is usually fine because everyone uses WhatsApp or iMessage over the eSIM data.

The eSIM profile itself is locked to the device that downloaded it. It cannot be moved to a second phone after install. If a buyer needs the same plan on a second device, that requires a new purchase. Some providers offer transfers as a support exception; most don’t. The published terms on each provider’s scorecard cover this — see the methodology page for how those terms are scored.

What an eSIM is not: a magic global connection. Coverage in any given country still depends on which local carrier the reseller has a wholesale agreement with. Speed in any given location still depends on that carrier’s network in that location. The reseller’s grade across the eight eSIMBench dimensions captures most of what differs between providers; the local network determines the rest.

For first-time buyers the right way to choose is to start from the destination and the duration: a 7-day trip with normal mapping and messaging use is a different problem than three months of remote work. The use-case rankings re-weight the dimensions for both ends of that spectrum and surface different top picks.