Warm Edge Spacer Guide
Complete comparison — Swisspacer Ultimate, Super Spacer TriSeal, Thermix TX.N, TGI vs standard aluminium. What a spacer does, conductivity, Psi values, edge condensation, colours, and when warm edge pays for itself.
What A Spacer Bar Actually Does
The spacer bar is the perimeter frame that holds the panes of a sealed unit apart at a fixed distance, forming the insulating cavity. It does three jobs at once: sets the cavity width, carries the desiccant that keeps the sealed airspace free of moisture so the unit never mists internally, and forms the base for the primary and secondary seals that keep the unit airtight for its working life. Because it sits at the very edge of the glass, in direct contact with both panes, its material has a disproportionate effect on how the unit performs thermally — far more than its thin cross-section suggests.
Warm Edge vs Aluminium
Traditional aluminium spacers have a thermal conductivity of 160 W/mK, creating a continuous cold bridge around the entire edge of every pane. Warm edge spacers replace that aluminium with a composite polymer, silicone foam or stainless-plus-polymer construction with conductivity as low as 0.17-0.19 W/mK — roughly 99% lower than aluminium. That difference is what eliminates the cold ring you can sometimes feel, or see fogging, around the edge of an older aluminium-spaced unit on a cold morning.
| Spacer | Material | Conductivity (W/mK) | Psi Value (W/mK) | Edge Temp vs Alu | Condensation | Colours |
|---|---|---|---|---|---|---|
| Aluminium | Aluminium alloy | 160.0 | 0.080 | Baseline (cold) | HIGH risk | Silver, White, Black, Brown, Grey |
| Swisspacer Ultimate ★ | Composite polymer | 0.19 | 0.030 | +3-4°C warmer | Very Low | Black, White, Brown, Grey, Oak +15 more |
| Super Spacer TriSeal ★ | Silicone foam | 0.17 | 0.028 | +3-4°C warmer | Very Low | Black, Grey |
| Thermix TX.N Plus | Stainless + plastic | 0.60 | 0.040 | +2-3°C warmer | Low | Silver / Black |
| TGI Spacer | Stainless + polymer | 0.90 | 0.050 | +1-2°C warmer | Low-Moderate | Silver |
★ CSU recommended. Available in all widths: 6, 8, 10, 12, 14, 16, 18, 20, 22, 24mm.
Condensation & Mould At The Edge
The edge of the glass, right where it meets the spacer, is the coldest point on any window — usually the first place internal condensation forms, ahead of the centre of the pane. With an aluminium spacer that cold ring runs a few degrees below the rest of the glass, which on a humid morning or in a poorly ventilated room is often enough to drop below dew point, producing the beading or misting you see in a band a few centimetres in from the frame on older units. A warm edge spacer raises that edge temperature by 1-4°C, keeping the pane closer to a uniform temperature and removing the damp micro-climate that black mould and sealant staining tend to establish over time — a genuine callback reducer, not just a comfort upgrade.
| Spacer | Uw (whole window) | Improvement vs Alu | WER Impact |
|---|---|---|---|
| Aluminium | 1.4 W/m²K | Baseline | Baseline |
| TGI | 1.35 | 3-4% | +2-3 kWh/m² |
| Thermix TX.N | 1.30 | 7% | +4-5 kWh/m² |
| Swisspacer Ultimate | 1.20 | 14% | +8-10 kWh/m² |
| Super Spacer | 1.18 | 16% | +9-11 kWh/m² |
The “Psi value” (Ψ) in the first table quantifies that edge heat loss — the extra heat lost specifically at the glass/spacer/frame junction, on top of the centre-pane U-value. A lower Psi value means less of the perimeter is acting as a cold bridge, which is why swapping spacer alone — with no other change to the glass build-up — measurably improves the whole-window Uw shown above, and can be enough on its own to lift a borderline unit into a better WER band.
Where The Heat Actually Escapes
The two cross-sections below show the same edge detail built two ways — aluminium spacer on the left, warm-edge composite on the right. Watch what happens to the heat path through the spacer bar, and to the interior glass edge on each side.
Colour Options
Spacer colour is a visible design choice as much as a technical one — it shows through the edge of the glazing bead on most frame systems, so it’s usually matched to the window frame colour rather than left as an afterthought.
| Spacer | Standard Colours | Best Match For |
|---|---|---|
| Aluminium | Silver, White, Black, Brown, Grey | Budget-led projects, standard frame colours |
| Swisspacer Ultimate | Black, White, Brown, Grey, Oak +15 more | Coloured/foiled frames, widest colour matching |
| Super Spacer TriSeal | Black, Grey | Contemporary black/anthracite frames |
| Thermix TX.N Plus | Silver, Black | Standard white or black frames |
| TGI Spacer | Silver | Traditional silver-line systems |
When Is Warm Edge Worth It?
Warm edge is our default recommendation across almost every project — the small uplift over aluminium is modest against the total unit cost, and it’s typically recovered within one to two heating seasons through reduced heat loss, before factoring in the reduced condensation and callback risk.
| Scenario | Recommendation |
|---|---|
| Any residential project, standard budget | Warm edge as standard — Swisspacer Ultimate or Super Spacer TriSeal |
| North-facing rooms, poor ventilation, high humidity (bathrooms, kitchens) | Warm edge strongly recommended — biggest condensation benefit |
| Coloured or foiled frame systems | Swisspacer Ultimate for the widest colour match |
| Commercial fit-out on a tight budget, low-risk elevation | Thermix TX.N or TGI as a mid-spec compromise |
| Heritage slim-fit units with restricted cavity depth | Warm edge recommended where the width allows — ask us to confirm fit |
CSU Recommendation
Swisspacer Ultimate or Super Spacer TriSeal for all projects. The marginal extra cost is typically recovered within one to two heating seasons through energy savings, and it eliminates edge condensation and the callbacks that come with it. Our spacer bar and unit components come mainly from Thermoseal Group and DGS — two of the UK’s largest IGU component suppliers — with other specialist suppliers used where a spec calls for it.Get a Trade Quote
Contact our sales team — quotes returned within 2 business hours (Mon-Fri, 8am-5pm).