Glossary

The industry hides behind jargon; here it is in plain language.

• Body impressionThe permanent dip a mattress develops where you sleep — the most common durability failure. Warranties only treat it as a defect past a stated depth threshold (commonly 0.75–1.5 inches, measured with no one on the bed). Many real-world sags that ruin sleep never reach the threshold, which is why the threshold number matters more than the warranty's advertised length.
• Coil gaugeThe thickness of a coil's steel wire. Counterintuitively, a LOWER gauge number means thicker, firmer, more durable wire (13-gauge is heavy-duty; 16–17 gauge is thin and springy). Support cores around 13–14.5 gauge suit heavier bodies; thin-gauge coils in cheap hybrids are a common early-sag culprit.
• Comfort lock (retailer-exclusive naming)The industry practice of selling the same mattress under different exclusive names at different retailers, making price comparison nearly impossible. The bed you tried at one chain often exists elsewhere under another name for less. Decoding these aliases back to the canonical model is a core function of this site.
• Fiberglass (in mattresses)Glass-fiber material some manufacturers use as a cheap fire barrier, usually woven into an inner sock beneath the cover. If the cover is opened or wears through, fibers can contaminate a home and are notoriously hard to remove. Labels are unreliable — 'fiberglass-free' claims have repeatedly proven false — which is why we only report fiberglass status we've verified against primary documentation.
• Foam density (lb/ft³)The weight of one cubic foot of foam, in pounds — the single best objective predictor of how long a foam layer lasts. For comfort-layer polyfoam: under 1.5 lb/ft³ is low, 1.5–1.8 is medium, 1.8+ is high. For memory foam: under 3.5 is low, 3.5–5 is medium, 5+ is high. Brands rarely advertise density on low-density beds — the omission is itself a signal.
• Hybrid mattressA mattress combining a coil support core with substantial foam or latex comfort layers (typically 2–3 inches or more). The coil base adds airflow, edge support, and durability versus all-foam builds; the comfort layers determine feel — and their foam density still determines how fast the bed ages.
• ILD (Indentation Load Deflection)A firmness measurement: the pounds of force needed to compress a foam sample by 25% of its thickness. Higher ILD = firmer foam. ILD measures how a foam feels on day one; it says nothing about durability — that's density's job. Two foams with identical ILD can age completely differently.
• Memory foam (viscoelastic foam)Polyurethane foam engineered to respond slowly to pressure, contouring to the body before recovering. Good pressure relief for side sleepers; the trade-offs are heat retention (unless gel or open-cell modifications work as claimed) and a 'stuck' feeling some sleepers dislike. Durability tracks density, just as with regular polyfoam.
• Pocketed coils (wrapped coils)Springs individually encased in fabric sleeves so each coil compresses independently. Better motion isolation and contouring than interconnected (Bonnell or continuous-wire) coil grids. Coil count matters less than marketing implies once past ~800 in a queen; coil gauge (wire thickness) matters more for support and longevity.
• Polyfoam (polyurethane foam)The most common mattress foam, made from polyurethane. Quality varies enormously and is best judged by density: low-density polyfoam (under ~1.5 lb/ft³) softens and sags quickly, while high-density polyfoam (1.8 lb/ft³ and up) holds its shape for years. Most 'mystery foam' in cheap mattresses is low-density polyfoam.
• Prorated warrantyWarranty coverage where, after an initial period, you pay a growing share of the replacement cost (often calculated from MSRP × years owned ÷ warranty length). A '10-year warranty, prorated after year 5' is really 5 years of full coverage plus 5 years of discounts. 'Lifetime' warranties are routinely prorated into near-worthlessness — always find the non-prorated years.
• Warranty code (law-tag code)A code some manufacturers print on the law tag indicating the real coverage structure — e.g. '10/10' (10 years, no deductible) versus '5/10' (deductible payments in years 6–10). Two beds with the same advertised '10-year warranty' can carry different codes and very different actual protection. Check the tag, not the ad.