A Small Material Shift with a Practical Purpose: HDPE in Our Covers

There is a familiar moment in the shop when the offcuts start to tell you something useful. In our case, the UHMW scraps were stacking up in ways that raised the same steady question every time we swept the floor: what are we supposed to do with all this. UHMW behaves well in the final product, but once it becomes waste it turns into a dead end. That reality shaped the direction of this update long before we changed a single toolpath on the Interrobang Manual Tonneau Cover.

The Story Behind the Switch

Interrobang has leaned on UHMW for years because it slides well, holds up to abrasion, and stays predictable through repeated cycles of loading and vibration. None of that caused trouble in use. The challenge came after fabrication. UHMW is difficult to recycle unless you are producing industrial volumes, and small shops rarely find a place in those systems. We searched for responsible options and reached the same answer each time: there was no practical path for our scrap.
So we returned to a material that helped get this whole project started. The first tonneau covers Bill made used HDPE because it was accessible, consistent, and familiar. Those early slides were CNC-cut from kitchen cutting boards, partly because they were available, and partly because they worked. Revisiting HDPE now has the same logic behind it, only supported by years of testing and a clearer understanding of what these components need to accomplish in a manual tonneau cover built for the Rivian R1T.

What HDPE Brings to the Build

HDPE shares many of the traits that made UHMW appealing. It machines cleanly, resists wear, and keeps its shape in the temperature swings that matter for truck beds. It has a naturally smooth surface that performs well in a sliding interface and accepts mechanical fastening without complication. For us, the standout advantage is simple: HDPE can actually enter recycling streams available to small manufacturers. Local recyclers can handle it, and in some cases we can repurpose the scrap ourselves into fixtures or small components that support the shop.
HDPE also maintains the performance expected from a Rivian R1T tonneau cover designed with daily use in mind. It keeps the track movement steady, the tolerances clean, and the interface consistent across repeated cycles of operation.

How HDPE Compares in Practice

In use, HDPE performs on par with UHMW for this specific role. The parts stay stable. The slides track as intended. The material does not introduce noise or movement that would compromise the system. Our testing confirmed what we expected from working with it years ago: it does the job cleanly and without surprises. For readers who want a deeper look at UHMW as a material, we covered its characteristics in an earlier post, available here.

Why This Change Makes Sense for Our Shop

A material choice is rarely just about the part itself. It affects how the shop runs, how waste is handled, and how much room there is to improve the design over time. HDPE gives us more flexibility on all of those fronts. We can recycle it locally instead of storing bins of offcuts that have nowhere to go. We can test small batches without worrying about creating waste we cannot responsibly deal with. Most importantly, it lets us build with confidence about where our materials end up once they leave the router.
There is also the possibility of turning our own scrap into something new. HDPE can be chipped, pressed, or remolded with relative ease. We have begun experimenting with ways to repurpose the excess into fixtures, shop tools, or small accessories that support our workflow. Nothing polished yet, but each trial opens the door for a more sustainable process.

What This Means for Future Builds

The shift to HDPE does not mark the start of a redesign. The covers still install the same way, slide the same way, and carry the same expectations for durability. What changes is the efficiency of the process behind them. When a material supports both the build and the shop that produces it, the work settles into a more reliable pattern. This gives us room to refine details, explore accessories, and keep developing custom Rivian accessories that behave the way they should.
This kind of decision rarely shows up on a spec sheet, but it shapes the way we work. It aligns with how Interrobang started, how we want to operate, and how we think small manufacturing should function.

Looking Ahead

As we continue refining the tonneau covers and exploring new projects, decisions like this guide the direction of our shop as much as our designs. HDPE keeps the product strong, keeps our workflow cleaner, and gives us a more responsible way to handle what we produce along the way.
If you have thoughts on this update or want to know more about how we choose materials for our Rivian tonneau cover projects, reach out. We appreciate the curiosity and the questions that help us build better.