The Comfort Index noise score on every Estimia profile is a quick translation of the technical Rw rating — the weighted sound reduction in decibels — into a number you can compare without doing acoustic maths. A 10 is a heavy laminated acoustic unit fit for a tram-line flat; a 4 is a plain double-glazed window. The sections below explain what the rating measures, what each step feels like at night, and which window choices actually move you up or down the scale.
Rw is the laboratory-weighted sound reduction of the glass unit, measured in decibels. A standard double-glazed window sits around 28–32 dB Rw. A good asymmetric acoustic unit reaches 38–42 dB; a heavy laminated acoustic unit for a noisy facade can hit 45–47 dB. The decibel scale is logarithmic — every three extra decibels roughly halves the perceived loudness of outside noise — so the jump from 30 to 40 is the difference between hearing every word a neighbour says and hearing a vague murmur. The Comfort Index maps that range onto a familiar 1–10 scale so a tram-line flat and a quiet cul-de-sac can be compared on the same axis.
The Comfort Index reads the Rw figure straight off the manufacturer's data sheet and maps the typical residential range onto a 1–10 scale. Roughly: Rw 35 dB maps to 1, Rw 38 dB to about 3, Rw 42 dB to 6, Rw 45 dB to 8 and Rw 50 dB to 10. The exact number matters less than the comparison: two windows three points apart on the index will feel meaningfully different at 3 a.m.; two windows one point apart probably will not.
Stand by a kerb on a busy two-way street and the sound level is around 75 dB. A 5/10 window (Rw ≈ 38 dB) drops that to about 37 dB inside the room — the level of a quiet office; you still hear every truck and every loud conversation. An 8/10 window (Rw ≈ 45 dB) drops it to around 30 dB — the level of a quiet library; the same trucks become a low whoosh, voices become unintelligible mumbles. For light sleepers, the difference between 5/10 and 8/10 is often the difference between earplugs and no earplugs.
Three parts of the construction do most of the work. First, asymmetric panes — for example 4 mm outside and 6 mm inside. Two identical panes share a band of frequencies where they both vibrate freely and let sound through; mixing thicknesses spreads those weak spots and is worth three to four decibels with no extra cost. Second, a wider chamber on the street side, ideally filled with argon: low-frequency rumble (trucks, buses, AC compressors) hates a deeper cushion. Third — and the single biggest acoustic upgrade — a laminated pane on the inside or outside, where a soft plastic film between two thinner panes swallows vibration before it can travel into the room.
For a quiet residential street or a courtyard-facing flat, a Comfort Index noise score of 5 or 6 (Rw 38–42 dB) is the sensible default. For a busy avenue, a school nearby or a city centre with active nightlife, aim for 7 or 8 (Rw 43–46 dB). For windows that face a tram line, a metro vent, a train track or a motorway, target 9 or 10 (Rw 47–50 dB) and insist on a laminated outer pane. Pushing further than 10 buys diminishing returns — at that point most of the remaining noise sneaks in around the frame, not through the glass.
Sound finds any gap. A 9/10 window in a sloppy install will still leak noise around the perimeter — full-perimeter foam, sealed reveals and a properly compressed gasket are non-negotiable. Trickle vents in the frame are tiny acoustic holes; if you need fresh air without opening the window, ask for an acoustic-rated vent (around 35 dB Dn,e,w). A plain vent can undo most of the work the glass does.
The Comfort Index reads steady-state airborne noise — traffic, voices, street music. It does not measure structural noise (footsteps from the flat upstairs, plumbing in the wall), which needs decoupled floors and pipe wraps, not windows. It also smooths over the difference between Rw and the spectrum adaptation terms C and Ctr that appear on detailed acoustic specs. For most residential decisions the single index number is enough; for a project beside a flight path or a rail line, ask for the full Rw (C; Ctr) triplet.
FAQs
For sleep on a noisy street, yes — every extra point matters. For a quiet suburb the upgrade pays back slowly, since you cannot hear the difference between 6/10 and 8/10 when the street is already silent. Match the target to the actual noise environment outside the window.
It is on the glass-unit data sheet, usually as "Rw" with a value in dB. Detailed specs list "Rw (C; Ctr)" — a triplet of numbers — where Ctr is the most relevant for traffic noise. If a quote does not state Rw, ask. A serious installer always publishes it.
No. Windows handle airborne noise that arrives through the wall opening. Footsteps and plumbing travel through the building structure and need different fixes — acoustic ceilings, decoupled floor underlay, pipe wraps. The Comfort Index says nothing about structural noise.
Yes — that is its single biggest selling point. The same soft plastic film that swallows vibration also holds the glass together if it cracks. A ground-floor window or a balcony door benefits twice from the same upgrade.
Often, yes. If the frames are in good shape and accept the thickness of an acoustic unit (usually 36–44 mm), a glazier can swap the sealed unit. Expect 30–40% of the price of a full window replacement, with most of the noise benefit.
On their own, PVC is marginally better because it dampens vibration where bare aluminium rings. But the glass package decides almost everything — a heavy acoustic unit in a thermally broken aluminium frame beats a plain unit in PVC by a wide margin. Focus on Rw, not the frame material.
