A loop-top fence (sometimes 'rolled top' or 'loop and spear') runs each vertical tubular bar up over the top rail in a smooth bent loop, then back down to the rail. The result is a continuous wave of loops along the fence top with no graspable horizontal and no pointed spear.
Loop tops are the politest-looking pool-compliant fence top because they avoid the spear's institutional look. They're also slightly more expensive to make than spear tops because each bar has to be bent on a tight-radius former rather than just cut and capped.
The AS1926.1 non-climbable zone applies above and outside the fence. A loop top satisfies the no-graspable-top requirement only when the loop diameter is small enough not to give a hand-grip (most suppliers specify 35 mm or less).