In-Depth Review: UnderCover Flex Tonneau Cover

The UnderCover Flex is a hard tri-fold tonneau cover that offers a plenty of flexibility and convenience for most makes and models of trucks. It also comes in at mid-range price point when compared to other covers in its class. But does the UnderCover Flex measure up to the needs of truck owners that expect the most from their trucks? Pretty much. After careful review, here’s what we found out.

Main Features

  • Low-profile flush fit with a UV protective black finish
  • Made of heavy-duty FRP panels
  • Weather and water resistant
  • Easy to install and quick to remove

Competitive Products

  • BAK BAKFlip MX4 Hard Folding Truck Bed Tonneau Cover
  • TURBO SII Tri-Fold Truck Bed Tonneau Cover
  • Rough Country Hard Tri-Fold Truck Tonneau Cover

What We Like

  • Smooth folding movement
  • Easy clamp-on design
  • Drive while cover is in any position
  • 100% bed access while installed

What We Didn’t Like

  • Slightly leaks at front of bed
  • Rubber gussets don’t always lay flat
  • Heavy panels may require two people to install

Overall Design and Construction

At first glance, the UnderCover Flex may look like your average, run-of-the-mill hard tonneau cover, but in this case, it’s not about looks, but functionality. The low-profile design is made of three sections of fiberglass-reinforced polymer (FRP) and an aluminum top skin. The skin’s surface is a high-gloss black with a hair cell grain texture that is crack and scratch resistant, so you slide your gear across the surface without a twinge of guilt. And if you need to strap down some gear on the cover, it will take up to 300 pounds, as long as it is evenly distributed.

The surface may have a high gloss but doesn’t give off glare. Its UV resistance shields the panels from warping and fading, so the cover continues to fit properly while maintaining it’s good looks.

The UnderCover Flex is designed to be used, and driven, in any position, from completely flat, to folded and propped up with a pair of rods at the front of the bed. When flat, the cover fits flush, offering both water-resistant protection and theft deterrence for the bed’s entire contents. When closed, a pair of integrated drain tubes help to whisk water away from the seams, and due to it’s flush-fit design, the tonneau cover cannot be opened when the tailgate is shut.

Finally, UnderCover prides itself with the fact that their cover will fit just about any truck bed and work seamlessly with your existing bed coating, including under-the-rail liners, spray-ins, and even tailgate caps, to keep your gear safe and dry. And if you need to need to remove the cover, all it takes is a few minutes to loosen the clamps.


No tonneau cover is worth it’s price if it doesn’t have some outstanding features, and the UnderCover Flex has several that should be attractive to any truck owner. Strong, durable, and water resistant are just the beginning.

With a standard rail system, the UnderCover Flex makes for easy installation and removal. While on, it offers full bed use, a pair of prop rods to keep the cover secure when hauling large loads, and a pair of slam latches that can be accessed from either side of the bed.

The bottom of each panel is covered with a durable aluminum skin which protects it from loose cargo and other debris, a protection that comes in handy when driving your truck when the cover is in one of the folded positions.

Finally, the UnderCover Flex tonneau cover is made in the United States and is backed by a 3-year manufacturer’s warranty.


When it comes to convenience, UnderCover has hit the mark with the Flex. All your have to do is pull a cable at one of the cover’s sides, flip, and then latch. It only takes a couple seconds to take the cover from its flat position and have it folded up securely in any position you need.

The UnderCover Flex will keep your bed dry, just don’t expect a water-tight seal. The rubber gussets and rail system does a good job in wicking away the water from the sides and down through the drain tubes, but some water will more than likely trickle into the front corners of the bed. And, as the cover ages, you’ll have to keep an eye on the gussets to ensure that they remain flat. Some owners report that the UV protection doesn’t extend the rubber seals.

Overall, the bed security is great. Close the tailgate, then close the lid and you can be assured that no one is getting into the bed without a key. The only drawback to the way the Flex is designed in this regard is that the tailgate must be closed before you can lay the cover flat.


The UnderCover Flex comes ready to install and is a pretty straightforward process that should take no more than 30 minutes. All it takes is to mount a pair of rails on either side of the bed, place the drain tubes and weather stripping, then lay the cover itself into place, and then tighten it down once you find the desired position.

The UnderCover Flex panels are heavy, so it may take more than one person to lay out the cover properly. Also, it may take several attempts to get the rails in the right position so that the cover lays flush against bed and maintains a tight seal at the front and back. But with a little patience, you should have the cover on your truck in no time at all.


Finding a tonneau cover that completes the balance between quality, price, and functionality is no easy task. The UnderCover Flex may not do that perfectly, but it does come close. UnderCover has established itself as one of the leading tonneau cover manufacturers and the Flex is yet another reason they are always at or near the top.

The Flex offers a high level of protection to your truck bed. As long as you are mindful of the possibility of small leaks at the front of the bed, your gear with stay dry. And with a locked tailgate, your gear is more secure than if it were in the cab.

If you are looking for a hard trifold tonneau cover that hits all your needs yet doesn’t break the bank, the UnderCover Flex just might be the right one for you.

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