Creating a smooth surface on a string so it wont squeak when the finger is moved across it is done in two ways. First, if you would imagine a circle, then cut it in half. The flat side would face out, with the circle side facing in. This is known as "Half Round." The second way is to use a flat winding instead of round winding.

Although great for recording/performing because there are no squeaks, the problem is 1) there is less mass which gives less tone 2) less mass causes less durability so the string wears out faster, much faster in some cases. Although some recording strings are at 95% of sound and durability to normal strings. Best advice = Try more than one recording string to see how you like them.
ECG23 (0.010)ECG23 (0.010)
ECG24 (0.011)ECG24 (0.011)
ECG25 (0.012)ECG25 (0.012)
ECG26 (0.013)ECG26 (0.013)