Backer Rods & Their Applications: Open vs. Closed Backer Rods


Backer rods are an invaluable part of many installations which will require caulking or sealing, from windows to concrete panels.  These rods are flexible pieces of foam that are inserted into a joint which will be filled with sealant.  They create a backstop, limiting the amount of sealant needed, but without compromising the seal being created.

These backer rods are usually round, although they do occasionally come in other shapes -such as squares or hexagons- for specialty applications.  Their most important attribute is their construction, specifically whether they are “open cell” or “closed cell.”  These two types of backer rods have very different applications, and it’s important to understand the differences between them.

Closed Cell vs Open Cell Backer Rods: What’s the Difference?

2.5 Inch Backer Rod

  1. Closed Cell Rods

Closed cell backer rods are designed to be impermeable.  Both the outer shell and the inner “cells” of material are kept entirely separate with hard barriers between them.  The most direct benefit this brings is that closed cell rods will not wick or absorb water, making them the right choice for applications such as window sealing which will be exposed to high moisture or humidity.

In addition, this closed design gives them a superior surface for adhesion, making it easier for many types of caulks and sealants to bond.  In some cases, this can result in a better seal at the end of the job.

  1. Open Cell Rods

On the other hand, open cell backer rods offer unrestricted airflow, allowing them to easily compress to very thin strips, then return to their normal shape once pressure is removed.  So, open cell rods are generally the right choice in applications where a large amount of movement is expected, or compression will be necessary.

The way these rods allow for airflow also makes them a good choice for applications where the caulk or other sealant needs to cure quickly.  More airflow allows it to dry smoothly from both sides and can substantially reduce curing times.  However, they should not be used with sealants which will be susceptible to bubbling from air passing through the backer rod.

Metro Sealant Supports Your Construction Projects

Metro Sealant is a family-owned company that specializes in sealing and waterproofing products, along with a range of PPE and other accessories that will make your job go easily.  We love taking on new challenges!  If you have a tough sealing problem, contact us for a consultation.