Learn about HDPE Innerduct from Experts

May 12, 2021

Forklift moving HDPE innerduct

Innerduct refers to smaller diameter conduits (i.e., ducts, conduit, or tubes) that are used to divide larger conduits into subsections. They facilitate the proper placement and positioning of fiber optic cables in underground conduit systems.

While innerduct can be manufactured from various materials, high-density polyethylene (HDPE) is the most preferred and common. HDPE innerduct offers a variety of advantages over other innerduct options, such as high tensile strength, low stretch and elongation, and good UV resistance. For these reasons, it is used in many communication, data, and other fiber optic cable applications.

Given the critical role HDPE innerducts play in underground conduit systems, it is essential to select the proper type and size and install them correctly. Otherwise, they may not operate or perform as intended. Below, we provide answers to some of the most commonly asked questions about HDPE innerducts to serve as a resource for readers that need assistance choosing and using them.


How Do I Determine the Required Diameter of Innerduct?

The innerduct diameter required for an application depends on the cable placement method. If the cable will be pulled into the conduit, the inside diameter of the innerduct should be two times the outside diameter of the cable. If the cable will be blown into the conduit, the cable should be slightly smaller than the primary conduit.

How Do I Determine the Required Dimension Ratio (DR) of Innerduct?

The innerduct Dimension Ratio or wall thickness required for an application depends on the Innerduct installation method and cable size being installed inside of it. When directionally drilling or plowing in the Innerduct, the forces placed on the Innerduct should not exceed the Safe Working Load Guidelines. If installing a longer distances or in tough soil conditions, a smaller DR or thicker wall is recommended. Balancing the Diameter and Dimension Ratio for installation and cable fill ratios should be considered. or the Plastic Pipe Institute Conduit Design Calculator are helpful resources when selecting the appropriate Innerduct dimensions.

How Many HDPE Conduit Innerducts Fit in a Casing Pipe?

The number of HDPE innerducts that fit in a casing pipe depends on the casing installation. If a run is straight and short, then more innerducts can fit in the casing pipe. If a run is complex and long, then fewer innerducts can fit in the casing pipe.

In general, the recommended percentage fills are as follows:

  • Max value: 70%
  • Short, straight runs: 50%
  • Long, complex runs: 30%

These values can be adjusted as needed depending on previous experiences.

Is Innerduct Available With More Than One Color or Length per Reel?

Yes, WL Plastics manufacturers Segmented Reels where multiple Innerducts are packaged in multiple compartments within the same reel. WL Plastics can make 2-way, 3-way, and 4-way segmented reels with different color combinations in each segment. Some manufacturers offer a Parallel Reel, where multiple conduits are freely wrapped around a single reel compartment. WL Plastics does not offer Parallel Reels to ensure quality of our products when they arrive to customers. Segmented Reels offer installers safer handling of the pipe as it comes off the Reels compared to Parallel Reels.

Is Innerduct Available in Coils Without a Reel?

Yes, WL Plastics’ Innerduct is available most commonly on reels, but can offer coils or straight lengths of Innerduct. Coil lengths vary with Diameter size and are banded together for safe handling. Coils often require different installation handling equipment than Reels. Straight lengths are only available for Conduit greater than 6’’ in diameter.

Why Can’t I Get Schedule 40 Products Greater than 3’’ on a Reel?

WL Plastics has chosen not to offer Schedule 40 wall thickness products greater than 3’’ to ensure integrity of the inside diameter and quality of our products. As pipe is wound onto the Reel from WL’s manufacturing process, tensile forces affect the Innerduct. With the thinner walls of Schedule 40 products in larger diameters, product could be prone to kinking or folding on the Reel.

Is a Ribbed or Smooth Innerduct Better?

Smooth Innerduct is the industry standard product and works in all application types with all cable installation methods. Theoretically, ribbed innerducts have longitudinal ridges on the inside diameter of the Innerduct that should reduce surface area and, consequently, friction. Industry Ribbed designs differ and offer different friction reduction amounts. WL Plastics recommends a friction reducing lubricant to be used at the time of cable installation regardless of Smooth or Ribbed Innerduct design.

Can I Source Products with Pull Tape Pre-Installed in the Innerduct?

Yes, WL Plastics offers factory pre-installed pull tape products. The Innerduct is extruded over the pull tape at the time of installation and tied off to the reel for easy access during installation. WL Plastics offers 1,000#, 1,250#, 1,800#, and 2,500# tape. Detectable tapes also available upon request.

Reel of HDPE innerduct

Learn More About HDPE Innerducts From the Experts at WL Plastics

Want to learn more about HDPE innerducts? Ask the experts at WL Plastics! We manufacture a broad selection of HDPE conduit and pipe, including innerducts. For information on these products, check out our HDPE conduit page or contact us today.