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Flexalen SL

Straight Lengths for high volume networks
Flexalen SL pre-insulated straight length pipes
Flexalen SL pre-insulated straight length pipes

Flexalen secures all-embracing solutions for district heating, cooling and potable water networks. Next to our flexible range, we also produce semi-flexible Flexalen Straight Lengths, ideal for high-volume district heating and cooling networks. Flexalen SL optimizes the performance of your network, while offering considerable installation and operational advantages. 

Urban district heating systems with Flexalen SL

Flexalen SL was specifically developed for large-scale applications in urban district heating and cooling networks with all the benefits of Flexalen for large volumes. The Flexalen SL pre-insulated pipe consists of:

  • Polybutene (PB-1) medium pipe: a flexible polyolefin material that assures quick and reliable assembly, 50 year lifetime, while being the best in class for pressure and temperature rating as well as energy efficiency.

  • PE-based polyolefin foam for diameters OD 63 to 125mm, which minimizes the risk of water absorption due to its hydrophobic and closed cell structure. This ensures the insulation properties of Flexalen 600 are safeguarded over a long product lifetime.

  • Polyurethane (PUR) insulation for diameters OD 125 to 225mm, offering a high insulation value which results in significant energy savings.

  • Smooth High-Density Polyethylene (HDPE) casing to protect the pipe against any risk of outside damage.

Proven efficiency

Discover how Thermaflex effectively renovated the district heating network of Otopeni in Bucharest (Romania) in partnership with Veolia. Click here for the case study and letter of recommendation.

  • 4x faster installation compared to conventional systems
  • 75% savings on installation costs
  • 40% savings on total investment costs
  • 2,083 tons of annual CO2 savings

Why choose Flexalen SL pre-insulated pipes?

  • Corrosion-free
  • Fully homogeneous weldability, ensuring reliable connections
  • Semi-flexible
  • Stable performance over long service life
  • Dimensioning and network optimization services
  • Quick and simple installation
  • Light material, ensuring easy handling
  • 10 year product warranty
  • Fully recyclable (up to OD 125mm)

Technical support

Our technical support team and network engineers are ready to support you with:

  • Network design optimization
  • Network dimensioning
  • Precheck of design and parts during order
  • Calculation
  • Training
  • Technical assistance on site


Our Flexalen SL pre-insulated pipes are available as a single pipe system (OD 63 to 225mm), with or without oxygen barrier (up to OD 90). Flexalen SL pipes are delivered in lengths 11.8m (OD 63 to 125 mm) or 5.8m (OD 125 to OD 225mm).

  • Installation

    Easy quick and safe to weld

    Can be welded outside the trench and pulled into concrete ducts (renovation)

  • Specificities

    Semi flexibility

    Usable for both heating and cooling applications

    Full range of accessories

    Safe and secure operation

    Long lifetime expectancy

  • Pressure rating





  • Service temperature

    Wide temperature range

    Minimum -15°C

    Maximum 95°C

  • Additional information

    For more details contact Thermaflex or download the technical datasheet!

  • Availabilities

    Available with single carrier pipe

    Pipes in straight length of 6/12m
    Pipe diameters medium pipe OD63 – OD125 (fully flexible like Flexalen 600)
    Pipe diameters medium pipe OD160 – OD225 (semi flexible)


  KIWA certificate K8492801 welding process for plastic piping systems Flexalen 600 PDF 371 KB Preview Download Mail

This process certificate is issued by KIWA on the basis of BRL 5609 'pre-insulated flexible plastics piping systems for warm water distribution outside buildings'

Together with KIWA the welding process of electrofusion, polyfusion and butt welding is technical approved with product certificate stated requirements.


Radius 10 Km
200 Km
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