Flexible pre-insulated plastic piping systems are factory-manufactured systems consisting of carrier pipe(s), thermal insulating material, and a protective jacket manufactured as an integrated system. These piping products are typically supplied as coils in long continuous lengths and may also be supplied in straight lengths.


Flexible pre-insulated plastic piping systems were pioneered in Europe, where district heating and cooling systems are common, and energy efficiency has been at the forefront for many years. High-performance insulating materials minimize heat transfer through pre-insulated plastic pipes, making these piping systems highly efficient and sustainable.

In residential and commercial construction, there are many instances where heated or chilled fluid must be transferred either within or between buildings, sometimes over long distances. Pre-insulated potable water pipes are also used to protect water from freezing, or to conserve energy when hot water is transferred over distances, such as when buried in a slab under a building floor.


Pre-insulated piping systems are available in several configurations and may include one or more carrier pipes within a common outer jacket.

Examples include two equal-sized pipes for supply and return hydronic piping, larger individual pipes to reduce the overall system diameter, individual pipes for potable water where freeze-protection is required, and pairs of hydronic pipes combined with a single potable water pipe to supply both heating and drinking water to a building.

Other configurations are possible. In some cases, heat-tracing cable can be integrated into the piping system for freeze-protection.


Several of the plastic piping materials represented by PPI's Building & Construction Division are utilized as the carrier pipe within pre-insulated plastic piping systems. This includes certain HDPEPEXPE-RTPEX-AL-PEX, and PP materials.

These plastic carrier piping materials have a range of temperature and pressure ratings. Many of the piping materials (e.g., PEX, PE-RT) are rated for continuous operation at 180°F (82°C), whereas others (e.g., HDPE) are better suited for cold or chilled water applications. Plastic piping materials should never be used for steam systems or hot water systems with temperatures that exceed 200°F (93°C), and the pressure rating of each piping materials must be adhered to.

Insulation may be bonded or non-bonded. In the former, a bond forms between the insulation and the carrier pipe that exceeds the modulus of elasticity of the carrier pipe. In the latter, the carrier pipe is not bonded to the insulation, allowing it to move freely within the insulation. Bonded insulation helps to reduce longitudinal thermal expansion and contraction, while non-bonded insulation products may be more flexible. In all cases, the maximum thermal conductivity is 0.30 BTU·in./h·ft2·°F (0.04 W/(m·K) when measured in accordance with ASTM Test Method C177. 

The outer jacket is constructed of a watertight polyethylene material containing 2–3 % carbon black to provide protection from UV degradation. The jacket provides mechanical and moisture protection for these piping systems, protecting the insulation from contact with the ground or external moisture and from damage during and after installation.

The industry standard for flexible pre-insulated plastic piping systems is ASTM F2165.


Typical applications of flexible pre-insulated plastic piping systems include:

  • District heating/cooling hydronic systems connecting buildings to common sources of heated or chilled fluid
  • Heating systems with remote outdoor boilers (e.g., wood-fired or pellet)
  • Supply for heated glycol to outdoor snow and ice melting systems
  • Transfer of heated or chilled fluid within or beneath large buildings
  • Turf conditioning systems
  • Industrial applications for a variety of purposes
  • Geothermal ground loop collection systems, when remote from heat pumps
  • Municipal water service lines, especially those in shallow-bury installations
  • Temporary water supply lines for freeze protection

ASTM F2165 Standard Specifications for Flexible Pre-Insulated Plastic Piping

This industry standard applies to pre-insulated plastic piping systems commonly used to convey hot and cold fluids. These piping systems include carrier pipe, thermal insulation, and outer jacket manufactured as an integrated system.

Originally published in 2002, recent revisions proposed by PPI on behalf of its members resulted in significant improvements to the latest edition of the standard, published in January 2019. For example:

  • Expanded scope includes new applications
  • Requirements for jacket materials are added
  • Both bonded & non-bonded insulation types are included
  • New carrier piping materials such as PE-RT, PP-R, PP-RCT are added

As a result of these changes, when specifiers require compliance to ASTM F2165 for flexible pre-insulated plastic pipes, they can expect consistent performance. Information about ASTM F2165 is available at https://www.astm.org/Standards/F2165.htm


The traditional method of installing pipe for applications within or between buildings is to construct rigid metallic piping systems (e.g., copper, steel), fabricated on-site from individual straight lengths, typically welded or brazed, then insulated and covered with protective material. For buried piping, the application of the waterproof outer covering is expensive and adds additional time.

Each time a pipe direction needs to change, fittings are installed to reroute the pipe around obstacles or corners. And because these piping systems often experience wide temperature ranges, expansion arms and loops to accommodate for longitudinal thermal expansion are a critical part of the design and fabrication.

By integrating all components into one pre-manufactured assembly, flexible pre-insulated plastic piping systems can provide significant time and cost savings, as compared with field-manufactured insulated piping systems constructed on-site of individual components while ensuring consistent performance of the piping system.

Because plastic piping systems are often supplied in long continuous lengths (e.g., hundreds of feet), many joints and connections are eliminated. Further time savings are seen when flexible pipes are easily bent around obstacles or to follow undulations in the ground. Outdoor construction time can be reduced by more than 50%.

When properly buried, friction with the earth compensates for longitudinal thermal expansion/contraction forces of the buried pipes. This can often eliminate the need for expansion loops or arms.

Plastic carrier pipe transfers fluid with minimal pressure loss and provides reliable, long life with no corrosion or mineral build-up.

Plastic piping systems are joined without flame, reducing the risk of fire. Combined with the lighter weight of these piping systems, this can contribute to safer jobsites.

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