Mattress type describes what generates the support, and it is the layer under the comfort surface that defines it. A pocket spring mattress carries coils in individual fabric pockets, grouped into three, five or seven zones. A Bonnell spring mattress wires its coils into one connected unit. Memory foam and gel memory build the whole mattress from foam that contours under load, while natural latex uses a resilient plant-derived core. Foam and portable folding mattresses use block foam without springs. Type is independent of size and of feel, so the same construction appears across the New Zealand standard sizes and at more than one point on the Plush to Firm scale.