Why is my travel eSIM data slow?

Read the pattern first

• Slow only in one crowded place, fine elsewhere: the mast is busy.
• Slow indoors, better by a window or outside: the building is blocking the signal.
• Slow everywhere since the first day: look at your phone's settings.
• Slow everywhere after heavy use: look at the plan's terms.
• Slow on one app only: the problem is that app or its servers.

Vodafone describes congestion simply: it happens when many people are connected to the same mast at the same time, and it can slow you down even with full bars. Inside, thick stone walls, metal and energy-efficient glass make it harder for a signal to reach the phone. Neither is a fault with the eSIM. If nothing loads at all, that is a different problem, covered in signal bars but no internet.

Settings on your phone that hold data back

• Low Data Mode on iPhone: Apple says it reduces the quality of streaming content and pauses background tasks such as iCloud Photos updates.
• Low Power Mode on iPhone: Apple says it disables 5G except in some cases.
• Data Saver on Android: Google says most apps then get background data only on Wi-Fi.
• A VPN: Google warns that any VPN may reduce internet speeds.
• A preferred network type set to LTE or lower, under the line's mobile data options.

Each of these is useful on a trip, and some travellers switch them on to make the data last. Just remember they are on. A video that looks blurry under Low Data Mode is doing what Apple designed, and messages that arrive late with Data Saver on are waiting for Wi-Fi. Turn them off one at a time and test, so you know which one made the difference. Our guide to using a VPN while travelling explains when it is worth keeping on.

The network your phone picked

When the eSIM can use more than one local network, the phone chooses for itself on automatic. It does not always pick the one that is best where you are standing; it may cling to a network that was strong a few streets back.

The first fix is the one Apple gives for problems abroad: turn on Airplane Mode for about 30 seconds and then off, so the phone searches again and can pick the best network. If one operator is clearly slow in your area, you can pin another by hand for a while, as explained in manual or automatic network selection. Switch back to automatic when you move on.

5G is not a cure for this. Google says 5G speed and performance vary widely with the carrier's network and traffic, your location and even some phone cases.

The plan: limits you may have reached

Some plans reduce the speed after a certain amount of use instead of cutting you off. Apple warns about this with international data plans: if you go over the plan's limit, you might run out of data or notice slower network speeds.

If the slowdown started suddenly after a few heavy days and happens everywhere, check how much you have used against the plan's terms. Plans sold as unlimited are the usual case, and our article on what unlimited data means on a travel plan shows what to look for in the small print.

On a plan with a fixed number of gigabytes, what happens at zero is a different question, covered in what happens when your travel eSIM data runs out.

The distance your data travels

One cause sits outside your phone and outside the local mast. When a line roams, its traffic does not always go straight from the local network to the internet. A study by researchers from several European universities, who measured 4G roaming on 16 mobile networks in 6 European countries, found that operators commonly use home-routed roaming: the data travels back to the home network first, so the exit point to the internet is in the operator's home country.

The researchers found that this adds delay and makes web pages load more slowly, more so the further you are from that home country, and that the effect is strongest when you open services hosted in the country you are visiting.

You cannot change this from Settings. It depends on how the operator behind the eSIM has set up its roaming. What you can do is rule out the other four causes first, because they are far more common and all of them can be fixed. Snoozim's eSIMs connect through local networks, so the checks above apply in the same order.