Iplex Pro-fit® PB hot and cold plumbing system is flexible enough to be bent by hand, is extremely light weight, offers corrosion resistance, and eliminates water hammer noise. In particular, no brazing or soldering is necessary. When installed by a licensed tradesman, the system has proven to be both high quality and economical to use.


Flow Rates

Flow rates within a pipe system are affected by a number of factors including:

  • Pipeline design – i.e. how many fittings and changes of direction withinthe pipeline system.
  • Internal bore of the pipe
  • Smoothness of the bore.

Iplex Pro-Fit® pipe has a larger internal bore for equivalent plumbing pipe material sizes. This factor together with its inherently smooth bore means that polybutylene has exceptionally good water flow characteristics. Depending on the home reticulation design this could mean more water to the tap and better performance for the householder when using multiple appliances.

Internal Pipe Dimensions for Equivalent Pipe Sizes and Materials
Internal Bore for Cu equivalentDN 15 DN 18 = 12.5mm DN 16 = 11.4mm DN 15 class B = 10.8mm
Internal Bore for Cu equivalent DN 20 DN 22 = 17.6mm DN 25 = 17.7mm DN 20 class B = 16.9mm
    DN 20 = 14.1mm  


Flow Resistance

Example 1

A domestic plumbing pipe installation is 45 metres long and the required discharge is 6.0 litre per minute. What is the pressure drop over this distance ignoring any differences in height between the start and finish point?

This flow corresponds to 0.1 litres per second. Draw a vertical line from the bottom axis of the chart at 0.1 l/s and where it crosses the pipe line being considered read horizontally to the vertical axis. For a DN 18 PB pipe the reading can be estimated as 80 m loss per 1000 m (note this is a logarithmic scale) or (80 x 45 / 1000 =) 3.6 m per 45 m of pipeline. This converts to 35 kPa pressure drop (i.e. 3.6 x 9.8)

For the same flow in a DN 15 B copper pipe the loss becomes 160m per 1000 m which is 6.3 m per 45 m or 62 kPa pressure drop.

If there is a height difference multiply the vertical rise in metres over the pipe length by 9.8 to convert to kPa and add to the chart calculation. (A fall should be subtracted.)

Example 2

A pipe is to be installed to transfer 140 litre per hour between two tanks with a 1.8m height difference over a distance of 100 metes. What pipe is suitable?

This flow converts to 0.0389 litres per second. The head loss can be expressed as 1.8 x 1000/100 = 18m per 1000m. Interpolate to find the 18m point on the vertical axis remembering this is a logarithmic scale. Draw a line horizontally to the point where it intersects the 0.0389 l/s line. All pipes with flow lines to the right of this point would be suitable. That is DN 18 PB would provide a flows slightly greater than required whereas DN 16 PEX and DN 15 B copper would be less than required.

Heat and Pressure Performance

It is recommended that the Iplex Pro-Fit® system be installed in accordance with the manufacturers installation requirements, AS/NZS 3500 Parts 1 & 4 and any local by-laws with particular reference to the pressure and temperature relationship as described in AS/NZS 2642 and detailed in the table below. Iplex does not warrant or recommend the use of Pro-fit® in conjunction with heat-trace systems.

Pressure rating of pipes according to pipe material temperature (AS/NZS 2642).

Working Pressure
Working Temp
40°C 50C 60C 70C 80C (25 years under continuous use)
Max. Working Pressure
1600 kPa
1370 kPa
1200 kPa
1050 kPa
880 kPa
740 kPa


Thermal Conductivity

The thermal conductivity of plastics is generally lower than that of metals. It is the poor thermal conductivity of polybutylene that restricts the heat loss through hot water pipes and reduces the need for lagging. In addition, the rate of heat flow through a body is not just directly proportional to the thermal conductivity but also inversely proportional to the thickness. The wall thickness of the Polybutylene pipe further restricts heat loss.

Lagging of Polybutylene water pipes is required where the pipe is installed in chases or where it penetrates a concrete slab or to meet the energy efficiency requirements of the Plumbing and Drainage Standard AS/NZS 3500 Parts 1 & 4 and Building Code of Australia.

Also in particularly cold climates lagging is recommended where freezing can occur, for example, where pipe is exposed above ground.

Although polybutylene pipes have been shown to withstand freezing of water to a greater extent than many other materials, the pipe obviously is not useable if the water inside is frozen. 

Thermal Conductivity – Watt per metre Kelvin (W/m.K.)
0.14 0.35 401.00 0.60 47.00 to 74.00

Plastics pipes such as Iplex Pro-fit® polybutylene inherently have a muchlower thermal conductivity than metal pipes, for example copper, and therefore the R values are higher and heat losses are lower. 

Inherent R Values – Pro-Fit®
Size R Value
R = 0.011
DN22 R = 0.015

However, in those applications where AS/NZS 3500 requires copper hot water pipes to be insulated, it is also necessary to insulate plastics hot water pipes using a similar thickness of insulation. Note that the total R value of an insulated plastics pipe will be higher than an equivalent copper insulated with the same material. Heat losses will again be less for the plastics pipe.

Noise Reduction

It is well recognised that polybutylene pipe is highly effective at virtually eliminating water hammer and water travel noise in domestic plumbing applications.  Sound velocity in materials is a function of the density of a material and the E-Modulus (elasticity) of that same material. polybutylene’s superior performance when compared to other materials is outlined in the table below. 

Sound Velocity in Materials
  Density kg/m3 E-Modulus MPa Sound Velocity m/s
PB 0.93 350 620
PEX 0.95 600 800
Copper 7.20 110,000 3,900
Soft rubber 0.90 90 320