BAKFlip MX4 vs the Rivals: UnderCover Ultra Flex, FiberMax, LOMAX and Endure ALX

How we made this guide: picks and specs come from our catalog and fitment data, owner quotes come from verified reviews and the guide was drafted with AI help, then checked and edited by Trevor Hall.

Pick the BAKFlip MX4 (from $1,199.99) if you want the most-reviewed hard folding cover in this group, with 5,025 owner reviews and a 5-year warranty. Pick the UnderCover Ultra Flex (from $1,199.99) if you prefer its look and seal design. It starts at the same price and matches the MX4 on paper: UnderCover rates it at 400 lb, gives it a 5-year limited warranty and fits a dual-action tailgate seal and drain tubes. It has less owner history: 356 reviews at 4.6 stars against 5,025 for the MX4.

The other three rivals each win one job. The BAKFlip FiberMax (from $1,249.99) has a fiberglass top. The Extang Endure ALX (from $1,499.99) is rated for 500 lb. The LOMAX tri-folds start at $1,115.20. All are hard folding tonneau covers and none has a key lock of its own.

The seven covers side by side

The table lists what the spec sheets and product pages give us. Prices are the lowest part price for any truck we fit, so your truck and bed may cost more. LOMAX sells three tri-fold lines, so each gets its own row. Every cover here relies on a locked tailgate to keep the bed shut.

What they share

All seven are rigid folding covers that clamp to the bed rails without drilling. Every one latches as it closes, and none has a keyed lock of its own. The Endure ALX listing says so outright. On a BAKFlip the only way in is through the tailgate, so a locked tailgate is what secures the bed. If your tailgate does not lock, fit a tailgate lock before you rely on any of them.

None is waterproof. Each relies on seals (most also on drains) for the water that gets past. None is sold as waterproof. If you need the bed to stay bone dry in a downpour, read our guide to the most watertight covers before you choose between these.

BAKFlip MX4 vs UnderCover Ultra Flex

On paper this is the closest match in the group. Both start at the same price, $1,199.99 and $1,199.99. Both are rated for 400 lb spread evenly, both carry a 5-year limited warranty for the original owner and both wear a matte black finish. Both use a dual-action tailgate seal, so the tailgate opens and shuts with the cover latched. Both rely on seals plus drain tubes for the water that gets past.

The gap is the amount of evidence. The MX4 has 5,025 owner reviews on file averaging 4.6 stars and the Ultra Flex has 356 averaging 4.6, so the MX4 has far more owner history behind it. Pick on the price for your exact truck and bed, and check the part notes if your bed has a factory rail or track system.

Two other UnderCover covers sit nearby. The Flex (from $1,099.99) is the gloss black one, and the ArmorFlex (from $1,349.99) costs the most of the three. Both list integrated drains and a dual-action tailgate seal. Browse the whole UnderCover range if the finish matters to you.

Pick the MX4 if owner history matters. Pick the Ultra Flex if you like its look and are fine with fewer owner reviews to go on.

BAKFlip MX4 vs BAKFlip FiberMax

The FiberMax costs a little more than the MX4 at $1,249.99 against $1,199.99, yet it gives up two things on paper. Its closed cover is rated for 300 lb where the MX4 carries 400 lb, and its warranty is 3 years where the MX4 has 5. It also uses a conventional tailgate seal, so you shut the tailgate before the last panel. The MX4 has the dual-action seal for working the tailgate with the cover latched.

You pay for the material. The FiberMax has cut and puncture resistant fiberglass top panels in a textured gloss black, where the MX4 wears aluminum in matte black. Owners rate it well: 4.7 stars from 320 reviews against 4.6 from 5,025. One writes:

“Took me about 30 minutes to install and I like that it is locked when the tailgate is up.”

BAKFlip FiberMax owner · 5 out of 5 stars

Two owners in the reviews we checked say the cover runs short at the tailgate. One 3-star owner writes:

“It’s as far back on the bulkhead as it can go and the tailgate barely touches the rear seal.”

BAKFlip FiberMax owner · 3 out of 5 stars

Pick the FiberMax if the fiberglass top is the point. Pick the MX4 for the longer warranty, the higher load rating and the easier tailgate. For the older G2 and the discontinued F1, see our G2 vs MX4 comparison and the F1 vs MX4 comparison.

BAKFlip MX4 vs LOMAX

LOMAX sells three hard tri-folds, and a search for "lomax vs bakflip" has to pick one. The Stance (from $1,287.90) is the nearest match: 400 lb, ten locking points when closed and a 3-year warranty. It folds to two-thirds open or flat against the cab, and it costs more than the MX4 to start. The Professional (from $1,353.60) is rated at 500 lb with diamond plate aluminum panels, and it lifts off without tools when you need the whole bed. It fits fewer trucks than the others: GM, Ford and Tacoma beds only in our catalog, with no Ram, Tundra or Nissan part.

The standard LOMAX Hard Tri-Fold (from $1,115.20) is the one that undercuts the MX4 on starting price, and it comes in aluminum, diamond plate, carbon fiber or FRP finishes. Its maker builds removal as a one-person job. The standard one has no owner reviews on file and no published load rating, while the Stance has 257 reviews at 4.7 stars and the Professional 34 at 4.8. The MX4 has far more track record. Browse the LOMAX range and check the part for your truck.

Pick LOMAX if you want a finish choice, a 500 lb rating or a lower starting price. Pick the MX4 if the 5-year warranty and 5,025 reviews matter more.

BAKFlip MX4 vs Extang Endure ALX

The Endure ALX is the costliest cover here, from $1,499.99, about $300 above the MX4. For that it gives a 500 lb rating against 400 lb, four TPO panels and a 5-year warranty that matches BAK's. It is a four-panel design that opens two-thirds on the buckle straps, and fully with its prop rods. It installs in under an hour, and we list no keyed lock.

The MX4 folds flush against the cab for 100% of the bed. One owner who weighed the two chose the Endure ALX for its twist latch, which he finds more theft resistant. He also liked that the fully open stack does not rest against the cab. He noticed a little water in the bed and plans to add a tailgate seal. Both covers clamp on and both take about an hour or less to fit. Another Endure ALX owner liked the install:

“Installation was a snap, fits great, and looks amazing.”

Extang Endure ALX owner · 5 out of 5 stars

The review sample also holds a hard warning on water. A 3-star owner on a 2025 Silverado reports:

“Unfortunately, after washing my truck for the first time with the cover on, I noticed a significant amount of water intrusion into the bed.”

Extang Endure ALX owner · 3 out of 5 stars

Pick the Endure ALX if you stack heavy gear on the lid and want the load margin. Pick the MX4 if you want to save about $300 and have the full bed open flush to the cab. Our Extang range has other folding options if you want to compare more. For more hard folders at once, see our hard folding roundup.

What owners report: leaks, parts and fit

Owner text is the best evidence we have, and it is uneven. The MX4, FiberMax and Endure ALX are the three we counted, and the UnderCover and LOMAX covers were not counted. The counts below are keyword matches across the reviews we checked for each cover, so they show how often a topic comes up and do not measure how often a cover fails.

Water is the common thread for all three, and it comes up a little more often on the FiberMax. For the MX4, the damage count is mostly small parts such as bumpers and prop-rod clips. A 2-star MX4 owner says the drains did not help:

“Was hopeful this wouldn't be the case with the integrated drainage system, but it leaks around all the edges & between panels.”

BAKFlip MX4 owner · 2 out of 5 stars

Happier MX4 owners point to the low, factory look:

“This is a low profile tonneau cover and it looks like it was factory installed the design is so well thought out.”

BAKFlip MX4 owner · 5 out of 5 stars

For the full list of causes and fixes, read our BAKFlip MX4 review.

Which one for which use

Frequently asked questions

Which is better, the UnderCover Flex or the BAKFlip MX4?

The UnderCover Flex starts about $100 lower at $1,099.99 and is the gloss black option, but UnderCover backs it for 3 years against 5 for the MX4, and it has 390 owner reviews at 4.7 stars where the MX4 has 5,025 at 4.6. Pick the Flex for the gloss finish and the lower price. Pick the MX4 for the longer warranty and the owner track record.

What are people saying about the UnderCover Ultra Flex?

Owners rate it 4.6 stars from 356 reviews, and we have not summarized what they write. What we can say is that it starts at $1,199.99 and that UnderCover publishes a 400 lb rating, a 5-year limited warranty, drain tubes and a dual-action tailgate seal for it.

Which BAKFlip tonneau cover is best?

For most trucks the MX4. The FiberMax suits a fiberglass top, and the G2 suits a lower budget. The F1 is discontinued, so we do not suggest it.

Are BAKFlip covers universal?

No. Each BAKFlip is built for one truck and bed length, so order the part number for your year, make, model and bed. The same goes for every cover in this comparison.

Is the BAKFlip MX4 worth the money?

Yes for most owners who use the bed daily, if the tailgate locks. It costs from $1,199.99, with 4.6 stars from 5,025 reviews. Skip it if you need a dry bed in all weather.

Are LOMAX covers as good as BAKFlip?

We have not compared what LOMAX owners write. The Stance has 257 reviews at 4.7 stars and the Professional 34 at 4.8, against 5,025 at 4.6 for the MX4, and the standard Hard Tri-Fold has none on file. On specs, the Stance matches the MX4 at 400 lb while the Professional goes to 500 lb. The warranty is 3 years against BAK's 5.

Which of these can I leave open part way?

The FiberMax, Endure ALX and LOMAX covers have a two-thirds position held by straps or clamps, and all of them except the LOMAX Hard Tri-Fold and Professional also fold fully against the cab (those two lift off for the whole bed). The MX4 folds in stages and stands against the cab for 100% access. Do not drive with any folding cover partly open unless its maker says that is allowed.

Related guides

• BAKFlip MX4 Review: Is It Worth the Money?
• BAKFlip G2 vs MX4: Which Is Right for Your Truck?
• BAKFlip F1 vs MX4: Which BAK Hard Folding Cover Should You Buy?
• Best Hard Folding Tonneau Covers: Picks for Security, Budget and Racks
• Best Tri-Fold Tonneau Covers: Hard and Soft Picks Compared