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The Alitherm 400 system is perfect for a wide variety of projects, including both new build and refurbishment, residential and light commercial applications and is proudly made in Britain by Smart.

Alitherm 400’s design incorporates Smart’s innovative polyamide thermal break technology, which creates a barrier between the cold air outside and warm air inside significantly reducing thermal transmittance and enhancing the system’s overall U-value. The system is also fully compliant with changes to Document L of the Building Regulations, is rigorously tested to PAS 24:201 as standard and exceeds the requirements for weather resistance and security performance.

Alitherm 400


The Alitherm 400 window is the first thermally broken aluminium system to feature Smart’s pioneering coextruded glazing gasket. This means the beads are supplied with the glazing gasket post-extruded into the profile. This enables the Quick-Glaze beads to be simply tapped in on site, significantly reducing fabrication and installation time.

Available with a flush or chamfered profile, the slim lines of Alitherm 400 provide excellent weather and thermal performance, as well as the security assurance provided by PAS24 accreditation. While the flush, flat face option is suitable for off-set, face-mounted espagnolette locks, the chamfered design features a eurogroove, to enable in-line espagnolette locking mechanisms to be used.

alitherm 400 doors


For installers, Alitherm 400's new, Quick-Glaze Bead is simply tapped in on site with the gasket already in place (rather than beading followed by inserting wedge gaskets), making the installa-tion and glazing process faster, more straightforward and more cost effective. Smart Quick-Glaze Bead is available in Naturals col-ours White (WP), Black (BL) and Anthracite Grey (KL005).

Quick Glaze bead



Rated 5.0 out of 5 Andrew Beevers

...trumps the steel-type systems on thermal performance and cost.
The grasp of the importance of design and quality of manufacture from the Marlin Team is second to none.


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Technical advisors are on hand at the aluminium window and door showroom in Keighley in West Yorkshire

Unrivalled Quality Customer Service

Our high quality window and door products are backed by the same high quality customer service. Technical advisors are just a phone call away to answer all your questions no matter how technical.

Typical help provided includes:

  • Choosing the right product
  • Getting the right made to measure size
  • Help with ordering
  • Threshold advice

We provide a FREE sample service to assist with surveying decisions, design considerations, or planning applications – just pick up the phone and ask.

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Glazing and frame colour choice


Our aluminium profiles are polyester powder coated by our systems suppliers using the very latest paint application techniques guaranteed for 25 years.

Fully compliant to the latest June 2022 building regulations our standard double glazing is the exceptional light transmitting, energy saving ClimaGuard® A+ low emissivity (Low-E) glass manufactured by Guardian Glass.

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Why Choose Marlin Windows?

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