The two model Harrowby series is characterized by the Classic 520 innerspring, which is described as "the newest version of Serta's most popular innerspring system." These are continuous coils. Each row of coils is formed from one carbon steel spring wire. Continuous coils are the most durable type of mattress coil. Many mattresses keep their support for 20 years or more.
Continuous coils are consistently firm, but they can be made more firm or less firm by the number of turns in the coils. The original version of continuous coils transferred a lot of motion from one side of the bed to the other. Now the coils are lined up head-to-toe to isolate the motion. This reduces partner disturbance. Serta calls this TrueSense™ Design 2.0. It has 2-way motion isolation.
With perimeter rods around the top and bottom of the innerspring, these mattresses do not need foam encasement for edge support.
The fabric in the quilted cover of the Harrowby mattress models is not specified, but it is most likely polyester.
Between the quilted top cover of the Harrowby mattresses and the Classic 520 innerspring is the comfort layer of Cool Twist™ Gel Foam. This is not memory foam as in the other Perfect Sleeper models, but comfort level polyurethane foam. It is infused with liquid gel for a more fluid-like support to relieve pressure on the hips and shoulders.
Another foam layer differentiates the two Harrowby models. In the Harrowby Firm, this is support foam. In the Harrowby Plush, it is PillowSoft™ Foam.
Suitable foundations for the Harrowby Firm and the Harrowby Plush are platform beds, solid-top box bases, and adjustable beds. Being continuous coil mattresses, they will also work with box springs and wood slat bases. Serta suggests pairing these mattresses with one of their adjustable bases, such as the Pivot Head-Up Foundation or the Motion Essentials II Adjustable Foundation.
Serta covers the Harrowby Plush and the Harrowby Firm with a 10-year non-prorated warranty. Since these are continuous coil models, the springs should last well beyond that. If there is any sagging, it would be in the foam layers. Therefore periodic rotation is advisable. Some retailers have a sleep trial period of 100 days.
Serta Perfect Sleeper Harrowby Plush and Harrowby Firm
Serta International, Customer Service Department, 3 Golf Center #392, Hoffman Estates, IL 60169, 1-888-55-SERTA (1-888-557-3782)
Innerspring (continuous coils)
Continuous coil innerspring, comfort layers of gel-infused PU and soft or firm comfort foam, quilted cover
Quilted, fabric probably is polyester
Platform, slatted frame, solid top base, or adjustable bed
Simple, durable, inexpensive
100 nights through some retailers
Keep in sanitary condition, and provide proper foundation