Are Thermal Spacer Bars Worth It? Expert Insights

Written by Chris Alderson

If you fabricate, specify or install IGUs, you’ll know how often warm edge spacer bars, thermal breaks and window U-values come up in conversations with customers, system companies and building control.

The question behind all of that is simple:

Are thermal spacer bars genuinely worth specifying – commercially and technically – or are they just a “nice-to-have” upsell?

This article takes a practical, B2B-focused look at thermal spacer bars: how they work, how Edgetech’s warm edge solutions contribute to system performance and compliance, and what they deliver in terms of call-back reduction, specification confidence and long-term customer value.

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Understanding Thermal Spacer Bars in Double Glazing

A modern double or triple glazed insulating glass unit (IGU) typically consists of:

• Two or three panes of glass
• One or two gas-filled cavities (typically argon, sometimes krypton/xenon)
• A spacer bar around the perimeter, maintaining the cavity and forming a key part of the edge seal

Historically, spacer bars have been manufactured from aluminium. Aluminium offers strength and ease of processing, but it is also a highly thermally conductive metal. Standard materials data put aluminium’s thermal conductivity at around 160 W/mK. In an IGU, that means the spacer acts as a thermal bridge between the warm interior and cold exterior.

The result is familiar to anyone who has modelled IGU performance:

• Lower internal glass surface temperatures at the edge
• Higher linear thermal transmittance (Ψ-values)
• Increased risk of condensation at the perimeter
• Increased overall window U-values

Warm edge spacer bars are engineered to remove this weak point. Instead of metal, they use low-conductivity materials such as silicone foam, thermoplastics or composite laminates. Edgetech’s flexible Super Spacer® range, for example, has a tested thermal conductivity of around 0.15 W/mK and has been shown to be over 950 times less conductive than aluminium. That dramatic difference in conductivity directly improves edge performance.

According to EN ISO 10077, a spacer is considered “thermally improved” or “warm edge” when the product of its thickness and thermal conductivity (Σ d·λ) is ≤ 0.007 W/K. This criterion comes from the European standard, not from any one manufacturer. Edgetech’s warm edge systems, including Super Spacer, are designed and tested to meet or exceed this warm edge classification.

For IGU manufacturers and window fabricators, spacer choice is therefore not just a component decision – it is a fundamental design choice that sets the thermal performance ceiling of the entire system.

How Thermal Spacer Bars Improve System Performance

Window performance is expressed via U-values (W/m²K), but behind every headline figure is a combination of:

• Centre-pane performance (Ug)
• Frame performance (Uf)
• Linear thermal bridging at the glass edge (Ψg)
• Installation detailing

Traditional aluminium spacer systems drive Ψ-values up because the spacer creates a cold strip around the perimeter. In some aluminium-spacer configurations, testing shows that the majority of energy loss through the IGU occurs at this edge zone, not through the centre of the glass.

Replacing metal spacers with warm edge spacer bars:

• Raises internal edge-of-glass temperatures
• Reduces Ψ-values at the perimeter
• Lowers overall Uw and system U-values

Independent modelling and manufacturer data indicate that switching from aluminium to warm edge spacer bars typically delivers around 0.15–0.2 W/m²K improvement in whole-window U-values, with “up to 0.2 W/m²K” realistic in optimised configurations.

From a B2B perspective, that translates into:

• Stronger headline U-values in datasheets and marketing
• Greater confidence when value-engineering specifications to meet project targets
• Flexibility to maintain aesthetics or frame choices while still hitting thermal goals

In other words, thermal spacer bars give you extra performance “headroom” that is difficult to achieve elsewhere without redesigning the whole system.Advantages of Using Warm Edge Spacer Bars

What is Warm Edge

Condensation Prevention and Reduced Call-Backs

For many installers, condensation at the glass edge is a persistent customer complaint. It can lead to:

• Customer concerns about “failed units” even when the IGU is performing as designed
• Visible dampness and staining around reveals and sills
• Long-term mould growth and dissatisfaction with the installation

Condensation occurs when the internal glass surface temperature drops below the dew point of the indoor air. Aluminium spacer bars, with their high thermal conductivity, reduce edge temperatures and make this more likely.

Edgetech’s warm edge spacer systems improve this significantly. Comparative testing and thermal modelling show that Super Spacer can:

• Raise internal edge-of-glass temperatures by up to 65% compared with aluminium spacer systems in equivalent conditions
• Reduce condensation occurrence by up to 70%, particularly at the perimeter

For trade professionals, the implications are clear:

• Fewer condensation complaints at the glass edge
• Better perceived quality of the installation
• Reduced risk of costly call-backs and remedial visits
• Improved customer satisfaction and likelihood of repeat business or referrals

Instead of spending time explaining why “a bit of condensation is normal”, warm edge spacer bars allow you to offer a specification that genuinely minimises the risk at the design stage.

Durability, Edge Seal Integrity and Lifetime Performance

The spacer bar is integral to the edge seal system and long-term performance of the IGU. Its behaviour under thermal and mechanical stress affects gas retention and the risk of premature failure.

High-quality warm edge spacer systems, as used across Edgetech’s range, contribute to durability by:

• Reducing temperature gradients at the perimeter, lowering stress on glass and sealants
• Providing flexible, compliant materials that accommodate movement without compromising the seal
• Supporting consistent gas retention performance over time
• Helping minimise moisture ingress and protecting desiccant performance

While real-world lifespans depend on design, manufacturing quality and installation, specifying a proven warm edge spacer system is a straightforward way for IGU manufacturers and fabricators to:

Protect their reputation for long-lasting units

Reduce the probability of premature misting and warranty claims

Offer more robust performance guarantees to their trade and commercial customers

Warm Edge Materials and Technology: Options for Specifiers

Today’s warm edge spacer bars cover a range of technologies, allowing specifiers to select systems matched to project priorities and production methods.

Silicone foam spacers

• Highly insulating, flexible structural foam with integrated desiccant and vapour barriers.
• Exemplified by Super Spacer®, Edgetech’s non-metal, pre-desiccated warm edge spacer for both double and triple glazing.

Rigid thermoplastic spacers

• Glass-reinforced thermoplastic profiles supplied as rigid spacer bars, offering excellent dimensional stability and significantly lower thermal conductivity than aluminium.
• Represented in the Edgetech range by TruPlas, a rigid warm edge spacer bar designed for increased stability and strength in automated production.

Composite laminate spacers

• Non-metallic spacer systems using composite laminate technology to combine very low conductivity with reliable argon gas retention.
• Duralite® from Edgetech is a flexible, single-seal warm edge spacer using composite laminate construction, engineered to deliver the lowest conductivity in the range and excellent gas retention performance.

Across these categories, the common objectives are:

• Low thermal conductivity and compliance with recognised warm edge criteria.
• Proven compatibility with modern low-e coatings and insulated gas fills.
• Strong performance in EN 1279 and related durability testing.

For specifiers, the takeaway is that warm edge technology is mature, widely adopted and available in multiple formats within the Edgetech portfolio, making it straightforward to integrate into almost any frame system or project requirement.

Building Regulations and Compliance: Part L and Beyond

Building Regulations are increasingly driving glazing specifications. Under Approved Document L for England (2021 edition with subsequent amendments), residential windows must meet demanding U-value targets set by government, not by manufacturers.

Key figures from Part L include:

New dwellings

Notional window U-value: 1.2 W/m²K

Limiting window U-value: 1.6 W/m²K

Existing dwellings (replacements)

Maximum window U-value: 1.4 W/m²K, or Window Energy Rating (WER) Band B or better

Most systems on the market aim to comfortably meet or exceed the notional 1.2 W/m²K value for new build, and high-performance configurations can deliver window U-values in the 0.8–1.0 W/m²K range, particularly with triple glazing.

Warm edge spacer bars from Edgetech are a key part of the compliance toolkit:

They help system houses and fabricators hit target U-values without resorting to extreme glazing or frame specifications

They create headroom for design flexibility, such as larger glazed areas or particular frame aesthetics

They support future-proofing as regulations continue to tighten and as designers work towards net-zero-aligned building envelopes

For commercial clients, social housing providers and volume housebuilders, warm edge spacer bars therefore underpin portfolio-wide compliance strategies, not just individual window upgrades.

Cost–Benefit for Fabricators, Installers and Specifiers

On a component level, warm edge spacer bars represent a modest additional cost over aluminium. The real question is what that buys the trade in return.

Commercial advantages include:

Stronger product proposition

• Better U-values and WERs to differentiate your offer in a crowded market
• Clear, evidence-backed performance claims supported by Edgetech test data

Reduced after-sales costs

• Fewer condensation and comfort complaints at the glass edge
• Lower probability of premature IGU failure and associated warranty costs

Simplified compliance

• Easier to design windows that meet or exceed Part L requirements
• Scope to align with future tightening of standards without redesigning whole systems

End-user value story

• Clear narrative around energy efficiency, comfort and moisture control
• Easier justification for higher-value specifications across retail and commercial projects

Viewed over the life cycle of a product range or a project, thermal spacer bars are less an “optional upgrade” and more a strategic specification choice enabling better margins, reduced risk and stronger long-term customer relationships.

Edgetech’s Super Spacer: Industry-Leading Performance

Super Spacer® technology represents the pinnacle of Edgetech’s warm edge innovation. First introduced in 1989, it pioneered flexible foam spacer technology and has been refined through decades of testing and field use.

Key points from Edgetech’s Super Spacer data:

• Flexible silicone foam construction with integrated desiccant and vapour barrier
• Thermal conductivity around 0.15 W/mK
• Over 950 times less conductive than aluminium, dramatically reducing edge-of-glass heat loss
• Proven to raise internal edge-of-glass temperatures and reduce condensation in comparative testing

For fabricators and specifiers who want a warm edge solution with a long track record and extensive independent verification, Super Spacer sits at the top of the performance range.
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Frequently Asked Questions for the Trade

1. How do warm edge spacer bars differ technically from aluminium spacers?

Aluminium spacers have very high thermal conductivity (~160 W/mK), creating a cold bridge. Warm edge spacer bars use low-conductivity materials (e.g. silicone foam, thermoplastics, composites) with conductivities down around 0.15 W/mK in the case of systems like Super Spacer, and are designed to meet EN ISO 10077 warm edge criteria (Σ d·λ ≤ 0.007 W/K).

2. What typical U-value gains can I expect from switching to warm edge?

In most double and triple glazing configurations, moving from aluminium to warm edge spacer bars delivers around 0.15–0.2 W/m²K improvement in whole-window U-values, with “up to 0.2 W/m²K” achievable in optimised scenarios. This gain often provides the margin needed to reach specific Part L targets.

3. Do warm edge spacer bars eliminate customer condensation complaints?

They don’t remove indoor humidity issues, but they substantially reduce the risk of condensation at the glass edge by lifting internal surface temperatures. In comparative testing, warm edge systems show up to 70% reduction in condensation occurrence and much warmer edge temperatures than aluminium. This translates into fewer visual issues and fewer call-backs for installers.

4. Are warm edge spacer bars suitable for triple glazing and large units?

Yes. Warm edge spacer bars are widely used in triple glazed IGUs, curtain walling and large-format glazing. In fact, the greater the glazed area and edge length, the more important edge performance becomes. Warm edge spacers help maintain consistent thermal performance across these larger assemblies.

5. Is specifying warm edge primarily a marketing decision, or a technical one?

It is both. Warm edge spacer bars deliver a measurable technical benefit in U-values, condensation resistance and edge seal performance, and at the same time provide a clear marketing story around comfort, efficiency and Building Regulations compliance. For most trade businesses, they form part of a standard higher-value specification, not just an optional “upgrade”.