Every spec we print in a mattress, base or bedding review, defined in plain English — including the ones brands use loosely. 54 terms, written by the same person who scores the beds.

• A
• B
• C
• D
• E
• F
• G
• H
• I
• L
• M
• O
• P
• R
• S
• T
• W
• Z

A

Adjustable base

A motorized bed frame that raises the head and foot of the mattress. Needs a flexible mattress (all-foam, hybrid or latex); most traditional innerspring beds should not be flexed.

Airflow (breathability)

How easily air moves through a mattress. Coil units and open-cell or perforated foams breathe; dense memory foam traps heat.

All-foam mattress

A bed built only from foam layers — memory foam, polyfoam, latex or a mix — with no steel coils. Usually quieter and better at motion isolation, usually weaker at edge support.

B

Bed-in-a-box

A mattress compressed, rolled and shipped in a carton. Expect 24–72 hours to fully expand and a short off-gassing period.

C

Coil count

The number of springs in the support unit. On its own it means little — gauge, zoning and coil shape matter more than the raw number.

Coil gauge

Wire thickness in a spring. Lower numbers are thicker and firmer: 12–13 gauge is sturdy support, 15–17 gauge is softer and more contouring.

Comfort layer

The top few inches you actually feel — foam, latex, microcoils or fiber fill. It sets the feel; the layers underneath set the support.

Convoluted foam

Egg-crate-shaped foam. The channels add airflow and a slightly softer, springier response than a flat slab of the same density.

Cooling cover

A cover knit with phase-change material, graphite, copper or a high-conductivity fiber so the surface feels cool to the touch. It manages the first few minutes, not the whole night.

D

Deep pocket sheets

Fitted sheets cut for thick mattresses. Measure your bed height, including any topper, before buying — 15 inches is the common cutoff.

Density (foam)

Weight per cubic foot, in lb/ft³. For memory foam, 4 lb and up is durable; under 3 lb tends to soften and body-impress early. Density is not firmness.

Dual firmness (split)

One mattress with a different feel on each side, or two twin XL beds on a split king base, so partners can choose separately.

E

Edge support

How well the perimeter holds weight when you sit or sleep near the side. Strong edges make the whole surface usable and make getting out of bed easier.

Encasement

A zippered cover that seals all six sides of the mattress. Used for allergen and bed-bug protection; a standard fitted protector only covers the top and sides.

Euro top

A pillow top sewn flush under the cover instead of stitched on, giving a cleaner edge and slightly firmer initial feel.

F

Firmness scale

The 1–10 industry shorthand. 3–4 is plush, 5 is medium, 6–7 is medium-firm (where most sleepers land), 8+ is firm. It is subjective and body-weight dependent.

Flippable mattress

A bed with a usable surface on both sides, often two firmnesses. Most modern mattresses are one-sided and should be rotated, not flipped.

Foundation

The rigid base a mattress sits on — a slatted platform or box frame. Slats more than about 3 inches apart can void a foam mattress warranty.

G

GOLS / GOTS certified

Third-party organic certifications: GOLS for latex, GOTS for cotton and wool. They certify the material and its supply chain, not the whole finished mattress.

Gel-infused foam

Foam with gel beads or swirls added to absorb heat. It slows the warm-up rather than removing heat over a full night.

H

Hi-Lo base

An adjustable base whose whole deck raises and lowers in height, not just the head and foot. Useful for caregiving and mobility.

Hybrid mattress

A pocketed coil support unit topped with substantial foam or latex comfort layers. The most common premium build: coil support and airflow with foam contouring.

I

Innerspring

A coil-dominant mattress with a thin comfort layer. Bouncy and breathable, weaker at pressure relief and motion isolation.

L

Latex (Dunlop vs Talalay)

Natural rubber foam. Dunlop is denser and firmer with more support; Talalay is airier, springier and more consistent. Both sleep cooler and last longer than most polyfoam.

Law tag

The white tag you must not remove before purchase. It lists the manufacturer, materials by percentage and the build date — useful for verifying what you actually got.

Lumbar zone

Extra reinforcement — firmer foam, thicker wire or microcoils — under the lower back to stop the hips sinking and the spine bowing.

M

Mattress protector

A thin waterproof or breathable layer over the mattress. Almost every warranty requires the bed to be stain-free, so this is the cheapest way to protect the claim.

Mattress topper

A 2–4 inch removable layer that changes the feel of a bed you keep. It can soften a firm mattress; it cannot fix a sagging one.

Medium-firm

Roughly 6–7 on the firmness scale. The safest choice for combination sleepers and the most-recommended firmness for back sleepers.

Memory foam

Viscoelastic foam that softens with body heat and moulds slowly to your shape. Best-in-class pressure relief; the trade-offs are heat retention and slower response.

Micro-coils

Short pocketed springs used inside a comfort layer instead of foam. They add responsiveness and airflow without the dead sink of thick memory foam.

Motion isolation

How well the bed absorbs movement instead of transmitting it across the surface. The spec that matters if a partner or pet moves at night.

O

Off-gassing

The temporary smell from freshly unwrapped foam. Usually clears in a few days with the room aired out; CertiPUR-US foams are tested for emissions limits.

P

Pillow top

An extra padded layer stitched onto the surface for a plush initial feel. Adds height and softness, and can body-impress earlier than a tight-top build.

Pocketed coils

Springs individually wrapped in fabric so each moves alone. This is what lets a coil bed contour and cuts motion transfer versus a connected innerspring.

Polyfoam

Standard polyurethane foam used as transition and base layers. Responsive and cheap; low-density polyfoam is the most common cause of early sagging.

Pressure relief

How well a mattress spreads weight at the shoulders and hips instead of concentrating it. Side sleepers and lighter sleepers need the most of it.

Presets (adjustable base)

Saved positions on a base remote — zero gravity, anti-snore, TV, flat — plus programmable memory slots.

R

Response time

How fast a surface returns to shape. Slow response means you feel hugged and have to push out of the bed to move; fast response is easier for combination sleepers.

S

Sagging vs body impression

A body impression is a shallow surface dent (normal). Sagging is permanent loss of support, usually 1 to 1.5 inches or more, and is what warranties actually cover.

Sleep trial

The at-home window in which you can return the mattress. Read the fine print: required break-in periods, return fees, pickup terms and whether the trial resets on an exchange.

Split king

Two twin XL mattresses on one king footprint, so each side can move independently on adjustable bases.

Spinal alignment

Keeping the spine in a neutral line in your sleep position. Too soft and the hips drop, too firm and the shoulders and lumbar gap open up.

T

Tencel (lyocell)

A smooth, moisture-wicking cellulose fiber used in covers and sheets. Cool and slick against the skin compared with cotton.

Thread count

Threads per square inch of sheet fabric. Above roughly 400 it stops meaning much; fiber quality and weave matter more.

Tight top

A flat, non-pillow-top surface. Typically firmer at first touch and more resistant to early body impressions.

Tilt (adjustable base)

A head-tilt hinge that angles the pillow section forward, so you can read or watch TV without craning your neck.

Transition layer

The middle layer between the comfort foam and the support core. It stops heavier sleepers from bottoming out onto the coils.

Trial fee (return cost)

What a return actually costs you — restocking, pickup, shipping, or a non-refundable delivery charge. A free trial is not always a free return.

W

Warranty (prorated vs full)

A full-replacement warranty repairs or replaces at no cost; after the prorated period starts you pay a rising share of the original price. Check when the switch happens.

Weighted blanket

A blanket with glass-bead or pellet fill, generally sized around 8–12% of body weight, used for calming deep-pressure input.

White glove delivery

In-home delivery with setup and, usually optional, removal of the old mattress. Charged as a pass-through service — check whether removal is included.

Z

Zero gravity

An adjustable base preset that raises head and legs above the heart to reduce lower-back load. The most-used preset on almost every base we test.

Zoned support

Firmness deliberately varied along the bed’s length — softer at the shoulders, firmer under the hips — to hold alignment without adding overall firmness.