Under a tenth of a second, against six seconds for a viscoelastic core. Both figures are correct, and neither is better. They are answers to two different questions, and the only person who knows which question is being asked is the one lying down.
The spring unit
7 zones · 160 mm
One thousand and eighty-eight coils, 2.0 mm wire, seven zones from head to foot, each coil sewn into its own pocket. Steel is the only elastic element in a mattress that will cross thirty thousand cycles under a 140 kg roller and come back with its geometry intact.
Two of them, one millimetre each: under the ticking, and under the spring unit. A mattress is sold on its foam and bought on its springs, and it lives or dies on the millimetre of hot melt that holds either of them to anything else. Thin, and it starves under load. Thick, and it becomes a plate.