Originally Posted by dddd

Focus instead on buying a tube that has a relatively wide (as measured folded flat) actual width, do not trust what is printed on the box or on the tube.
Tubes are "sized" all over the place relative to their rated sizing, so better to compare the width as presented right out of the box in the flattened state.

Don't use a tube narrower than 30mm (measured folded) in a 27x1-1/4" tire or it will have to stretch considerably to fill the volume of the tire casing.
With the tube so stretched, tiny thorn-type punctures will be pulled open to allow rapid loss of air, versus being able to ride home without stopping for a road-side repair.
So it's worthwhile to seek out the widest tubes that can be installed in your tires without issues such as having folds in the tube that might cause thumping when riding at high speed.
Wider tubes will tend to be heavier, but a tube rated for 32-38mm is often the best choice for use in these 27" wheel bikes I've found.
Not that I like waking up to a deflated tire, but it beats the alternative of having to fix one out on the road in blazing summer heat or with rain threatening.