UnderCover Ultra Flex vs BAKFlip MX4: Which Wins? (November 2026)

On this page (8 sections)

1. UnderCover Ultra Flex vs BAKFlip MX4 at a glance
2. The matte finish and carpeted under-panels favor the Ultra Flex
3. Bed access and folding: both open fully, one props itself up
4. Security and weather sealing lean toward the MX4
5. Fit and truck coverage decide more than the specs
6. Who should buy the UnderCover Ultra Flex?
7. Who should buy the BAKFlip MX4?
8. Which hard folding cover should you pick?

The UnderCover Ultra Flex wins for most truck owners. It pairs a matte-black finish with carpeted under-panels, dual prop rods and a 5-year guarantee.

The BAKFlip MX4 is not the runner-up by much. In this undercover ultra flex vs bakflip mx4 comparison, the MX4 takes the win for F-150 and Ram 1500 owners who want lighter panels and BAK's upgraded auto-latching security.

Both are hard folding aluminum covers that fold toward the cab and give full bed access. The real decision comes down to your truck, your tailgate and how much you value the extras.

UnderCover Ultra Flex vs BAKFlip MX4 at a glance

The Ultra Flex is the more feature-rich cover, while the MX4 is the lighter, more security-focused one. The table below lines up the two families side by side.

The Ultra Flex name covers two fits here: the UX12019 for 2014-2018 and 2019 Limited/Legacy Silverado and Sierra 1500 plus 2015-19 2500/3500HD trucks with the 6' 7" bed, and the UX32010 for the 2020-2025 Jeep Gladiator 5' bed. The MX4 name covers the 448227 for the 2019-2026 Ram 1500 5' 7" bed and the 448339 for the 2021-2026 F-150 5' 7" bed.

The Ultra Flex pair carries scores of 9.7 and 9.4. The MX4 pair sits at 9.3 and 8.9.

That gap reflects the extra hardware on the Ultra Flex more than any big difference in the panels themselves.

The bed lengths are part of that story. The Silverado and Sierra 1500 version of the Ultra Flex covers the long 6' 7" (78.9") bed, while the Gladiator version is cut for the 5' (60") bed.

The Ram 1500 MX4 fits a 5' 7" (67.4") bed and the F-150 MX4 fits a 5' 7" (67.1") bed.

Longer beds mean more panels and more hardware, so a bigger cover is not automatically the better value, just the one that matches the truck.

The matte finish and carpeted under-panels favor the Ultra Flex

The Ultra Flex wins on finish and bed protection. Its durable aluminum panels come in a matte-black finish, and the cover sits flush mount to improve the look of the truck.

The bigger practical difference sits underneath, where the Ultra Flex ships with carpeted under-paneling for added cargo protection inside the bed.

If you haul furniture, tools or anything that scuffs easily, that carpet layer is real insurance against scratches from above. The MX4 counters with a textured matte-black finish across all surfaces and a flush-mount, low-profile look.

BAK builds the Gen 3 panels from aluminum with high-density polymer cores, and that construction is about strength, not cargo cushioning.

Why the carpeted panels matter in daily use

The carpet layer runs on the underside of the folded panels, so it faces the cargo side of the cover. Every time you slide a box or a bike under a closed cover, the panels sit directly above it, and on the Ultra Flex that contact point is soft.

The carpet also deadens some of the hollow drum sound you get when rain hits a bare aluminum panel.

That is a comfort detail rather than a strength one, but it is the kind of thing you notice on a long drive. The MX4's panel surfaces are finished for looks and durability, and its alloy construction and polymer cores are aimed at handling heavy loads and daily use.

BAK's description makes no cargo cushioning claim, so the MX4 is a cover that protects your gear from weather and theft, not one that pads it.

Neither cover wins on looks alone. If you want the bed to stay tidy underneath, the Ultra Flex's carpeted panels are the deciding feature.

If you only care about the view from outside the truck, the two finishes are close.

Bed access and folding: both open fully, one props itself up

Both covers give 100% bed access and can be driven fully open. The difference is how each one holds itself out of the way.

The Ultra Flex folds into an upright position on dual prop rods that lock into place and store away easily when not in use, and the cover does not rest on the back of the cab.

UnderCover says you can drive with the cover closed, partially closed or fully opened. The MX4 folds to the cab, secures there and lets you drive with the cover fully open.

BAK pitches this as no wasted bed space, parked or driving.

The Gen 3 also uses a click-in rail system that BAK says cuts install time by up to 12 percent. The prop rods are the more useful design for everyday hauling.

You can flip the cover up, lock the rods and load the bed without the cover leaning on the cab or blocking the rear window as much.

The MX4's fold-to-cab approach is simpler, with fewer parts to manage. If you open and close the cover several times a day, the Ultra Flex's rod system is worth the extra step.

If you mostly leave the cover closed and only open it for big loads, either design works.

Security and weather sealing lean toward the MX4

The BAKFlip MX4 wins on locking hardware and seal detail. BAK's Gen 3 design uses a patented auto-latch locking system that secures the cover automatically when closed, plus newly engineered lock components built to resist tampering and forced entry.

The MX4 also gets revised EPDM perimeter seals, all-new tight-fit clamps and a longer dual-action tailgate seal.

BAK says the cover was tested from -40 to 180°F and zero to 95% humidity, and backs it with a 5-year warranty. That is BAK's claim, not a lab result we ran ourselves.

The Ultra Flex is no slouch on security. Its automatic latches lock the cover into the bed's side rails and release from either side of the bed, and it also has a dual action tailgate seal, so you can close the tailgate with the cover up or down.

The difference is emphasis. BAK markets the MX4 around theft resistance and water intrusion, and the hardware reflects that.

UnderCover markets the Ultra Flex around versatility and cargo care. If your truck parks outside or carries expensive gear, the MX4's locking story is the stronger one on paper.

How the tailgate seals differ in practice

Both covers use a dual action tailgate seal. That means you can close the tailgate whether the cover is up or down, and the seal still lines up with the tailgate edge.

BAK describes its version as longer. A longer seal covers more of the gap between the cover's rear edge and the tailgate, which is one of the common places water sneaks in on a tonneau.

That extra length is part of why BAK calls its seal package the best one yet. The Ultra Flex's seal is built for the same convenience, but UnderCover does not make the same length claim.

For most owners the practical difference is small. If your truck lives outside in heavy rain and you keep gear in the bed year round, the longer seal is a point in the MX4's column.

Fit and truck coverage decide more than the specs

Your truck model is the real tiebreaker. These covers are vehicle specific, and the fit lists are narrow.

The Ultra Flex UX12019 fits 2014-2018 and 2019 Limited/Legacy Chevy and GMC Silverado/Sierra 1500 trucks, plus 2015-19 2500/3500HD models with the 6' 7" bed.

The UX32010 fits the 2020-2025 Jeep Gladiator 5' bed.

The MX4 448227 fits the 2019-2026 Ram 1500 with the 5' 7" bed, and it does not fit the multi-function split tailgate. The 448339 fits the 2021-2026 Ford F-150, including Raptor and Lightning, with the 5' 7" bed.

There is almost no overlap here. If you drive a Silverado or Sierra 1500 from those years, the Ultra Flex is the cover on this list built for you.

If you drive a 2021 or newer F-150 or a 2019-2026 Ram 1500, the MX4 is the fit.

Check your bed length and tailgate before ordering. A cover that does not fit your truck is not a better or worse cover, it is just the wrong part.

For a broader look at fit and cover types, our guide on which tonneau cover should I buy walks through the decision.

Weight and installation

The Ultra Flex UX12019 weighs 80 lb and the MX4 448227 weighs 71 lb. That 9 lb gap matters if you remove the cover often or install it alone.

The F-150 MX4 lists a maximum weight capacity of 54.9 pounds, which is about what the cover is rated to hold on top, not what it weighs. Keep it in mind if you plan to set gear on a closed cover.

Both install without special tools. The Ultra Flex uses L-Rails that also make removal easier.

The MX4's click-in rails are the quicker install of the two, according to BAK. Neither cover needs drilling into the truck bed, and both come with rails and hardware.

UnderCover backs the Ultra Flex with a 5-year guarantee. The F-150 MX4 carries an extended 5-year warranty, while the Ram 1500 MX4's spec sheet shows a 3-year warranty description alongside a 5-year warranty in its bullets.

Confirm the term for your exact model when you order.

What comes in the box

The Ultra Flex Silverado and Sierra version lists its included components only as auto parts, and the Gladiator version does not spell them out either. UnderCover's description names the cover, its L-Rails and the prop rods as the core pieces.

The MX4 listings are more explicit. The Ram 1500 version lists a truck bed cover, two side rails and a hardware pack.

The F-150 version lists the tonneau cover, a hardware kit and an install guide.

Who should buy the UnderCover Ultra Flex?

Buy the Ultra Flex if you drive a Silverado, Sierra or Gladiator and want the most cover for your money. The carpeted under-panels are the feature you will notice every time you load something scratch-prone.

The matte finish and flush mount keep the truck looking clean, and the dual prop rods let you drive with the cover upright without it resting on the cab.

UnderCover backs the cover with a 5-year hassle-free guarantee and a US-based support team.

The UX12019's 80 lb weight is the main trade-off. If you plan to remove the cover between seasons or install it without help, the MX4's lighter panels are easier to handle.

Owners of 2014-2018 Silverado and Sierra 1500 trucks get the strongest value here. The UX12019's 9.7 score is the highest of the four covers in this comparison, and it fits a wide spread of those trucks, including the 2500/3500HD with the 6' 7" bed.

Gladiator owners get the same build at a 9.4 score, with the shorter 5' bed cutting down the cargo space under the cover.

Who should buy the BAKFlip MX4?

Buy the MX4 if you drive a 2021 or newer F-150 or a 2019-2026 Ram 1500 and want the newer locking and sealing hardware. The upgraded auto-latch system is the centerpiece, and the tighter seals target water intrusion.

The MX4 is also the lighter option at 71 lb for the Ram 1500 model.

That helps with installation and removal.

The click-in rail system speeds up the install. Skip the Ram 1500 MX4 if your truck has the multi-function split tailgate.

The cover does not fit that tailgate, and no amount of sealing hardware fixes a fit problem. F-150 owners with a 5' 7" bed, Raptor and Lightning included, have a clean fit.

The MX4's 9.3 and 8.9 scores trail the Ultra Flex slightly. The gap is small, and for Ford and Ram owners the fit advantage outweighs it.

Our BAKFlip MX4 review for the F-150 digs into the F-150 model in more detail.

Which hard folding cover should you pick?

Pick the UnderCover Ultra Flex for most buyers, and pick the BAKFlip MX4 when your truck or your security priorities call for it. That is the short version of this undercover ultra flex vs bakflip mx4 decision.

The Ultra Flex wins overall on features and fit spread.

Its matte panels, carpeted under-panels, dual prop rods and dual action tailgate seal give you more cover for the same tier, and the 5-year guarantee and US-based support round it out.

The MX4 wins on locking hardware and seal detail. If your truck is one of the F-150 or Ram 1500 models it fits, and you want the newest auto-latch system, it is the better pick for you.

If your truck fits neither list, neither cover is right. Our comparison of the BAKFlip MX4 vs UnderCover Armor Flex covers another UnderCover option, and the MX4 vs Rough Country hard tri-fold comparison looks at a budget rival.

Start with fit, then choose by the extras you actually use.

Frequently asked questions

Is the UnderCover Ultra Flex better than the BAKFlip MX4?

The Ultra Flex is the better all-round cover for most buyers. Its matte finish, carpeted under-panels, dual prop rods and 5-year guarantee add up to more cover for the money, while the MX4 counters with lighter weight and upgraded auto-latching security.

Which cover keeps water out better, the Ultra Flex or the MX4?

The BAKFlip MX4 Gen 3 has revised EPDM perimeter seals, tight-fit clamps and a longer dual-action tailgate seal, so BAK puts the most emphasis on weather sealing. The Ultra Flex also uses a dual action tailgate seal, but BAK's seal package is the more detailed of the two.

Can I drive with either cover fully open?

Yes. Both covers fold toward the cab and can be driven fully open, and both give 100% bed access.

The Ultra Flex holds itself upright on dual prop rods without resting on the back of the cab, while the MX4 folds to the cab and secures there.

Does the BAKFlip MX4 fit a Ram 1500 with a split tailgate?

No. The MX4 for the Ram 1500 does not fit the multi-function split tailgate.

If your truck has that tailgate, choose a different cover or confirm fitment with the seller before ordering.

Which cover is easier to install?

Both install without special tools. The BAKFlip MX4 Gen 3 uses a click-in rail system that BAK says cuts install time by up to 12 percent, while the Ultra Flex uses L-Rails that also make the cover easy to remove.

How long is the warranty on each cover?

UnderCover backs the Ultra Flex with a 5-year hassle-free guarantee. BAK lists a 5-year warranty on the MX4 for the F-150 and Ram 1500, though the Ram 1500 model's spec sheet also shows a 3-year warranty description.