This is a question we get often, and the simple answer is that it depends on what you prioritise.
We think that a round cable is often the easiest choice in many standard installations. It is flexible, easy to work with and feels natural when the bulbs are meant to hang downward.
A flat cable, however, has other strengths. It is made of rubber, has slightly thicker copper wire and can handle somewhat higher wattage. That makes it a very good choice when you want an extra robust solution for outdoor use. If you are going to hang the string light from a ceiling, a flat cable is a very good choice since the flat surface follows the mounting surface perfectly.
We usually think about it like this:
So it is not really about one always being better than the other, but about which qualities matter most to you.
In many standard home environments, we think that a round cable is the most natural choice. It is lighter and more flexible, which makes it practical when hanging string lights over patios, pergolas, gardens and other areas where the string light is meant to hang freely.
A round cable often works well when you want:
A flat cable is a very good option when you want something more robust. Our flat cable is made of rubber, while the round cable is made of PVC. The flat cable also has slightly thicker copper wire, which means it can handle somewhat higher load and wattage.
That is one of the reasons why many of our business customers choose a flat cable.
A flat cable often works well when you want:

The biggest technical difference is therefore the material and construction.
Flat cable
Round cable