# BAKFlip MX4 vs UnderCover Ultra Flex: Which to Buy > BAKFlip MX4 vs UnderCover Ultra Flex: two upright hard folders compared on load rating, tailgate seal, racks, fitment and prices for the same trucks. - Source: https://truckcoverguide.com/posts/bakflip-mx4-vs-undercover-ultra-flex/ - Markdown version: https://truckcoverguide.com/posts/bakflip-mx4-vs-undercover-ultra-flex.md - Last updated: 2026-11-12 --- - [Home](https://truckcoverguide.com/) - [Guides](https://truckcoverguide.com/guides/) - BAKFlip MX4 vs UnderCover Ultra Flex: Which Upright Hard Folder Wins? Head-to-head # BAKFlip MX4 vs UnderCover Ultra Flex: Which Upright Hard Folder Wins? Updated November 12, 2026 By [Truck Cover Guide Editorial Team](https://truckcoverguide.com/about/) [How we research](https://truckcoverguide.com/how-we-research/) Prices are approximate and change often, so check the current price before you buy. ## Key takeaways - Both are hard aluminum folders that stand upright behind the cab, drive open, install without drilling and carry a 5-year warranty. Neither has its own key. - The **BAKFlip MX4** publishes a 400 lb rating and has far more owner ratings; the **UnderCover Ultra Flex** publishes no load rating. - The Ultra Flex's dual-action tailgate seal lets you shut the tailgate with the cover up or down, and it has a version for the Ram 1500 Multi-Function tailgate (the MX4 listing doesn't fit it). - The MX4 is about $100 cheaper on the F-150 5.5 ft, but on three of the five matched fitments we checked the Ultra Flex was the cheaper one. Compare the listing for your own truck. - For racks, BAK sells the MX4 TS; we found no maker-confirmed rack pairing for the Ultra Flex. ## Our top picks - 1![BAKFlip MX4 Hard Folding Tonneau Cover](https://truckcoverguide.com/_astro/bakflip-mx4.CoOqV3JL_1Hou5h.webp)Best for most owners: 400 lb rating, biggest owner base, about $1,200 for the F-150 5.5 ft[BAKFlip MX4 Hard Folding Tonneau Cover](https://truckcoverguide.com/tonneau-covers/bakflip-mx4/)Hard folding · Aluminum panels · 100% bed access · Locks with tailgate8.2**$$$**$PremiumPrice tier: Premium[Check price on Amazon](https://www.amazon.com/dp/B08L44X6NZ?tag=truckcoverguide.com-20) - 2![UnderCover Ultra Flex Hard Folding Tonneau Cover](https://truckcoverguide.com/_astro/undercover-ultra-flex.OQ-o4ux1_1HwnIY.webp)Best for tall loads and the Ram split tailgate: tailgate closes with the cover up or down, about $1,300 for the F-150 5.5 ft[UnderCover Ultra Flex Hard Folding Tonneau Cover](https://truckcoverguide.com/tonneau-covers/undercover-ultra-flex/)Hard folding · Aluminum panels · 100% bed access · Locks with tailgate8.1**$$$**$PremiumPrice tier: Premium[Check price](https://www.amazon.com/dp/B08L44F1TH?tag=truckcoverguide.com-20) ### On this page 13 sections - [Quick comparison](#quick-comparison) - [Bed access and everyday use](#bed-access-and-everyday-use) - [Security and locking](#security-and-locking) - [Load rating](#load-rating) - [Weather sealing](#weather-sealing) - [Installation](#installation) - [Bed racks and accessories](#bed-racks-and-accessories) - [Prices for the same trucks](#prices-for-the-same-trucks) - [Fitment: which one covers your truck](#fitment-which-one-covers-your-truck) - [Owner track record](#owner-track-record) - [Who should skip each one](#who-should-skip-each-one) - [BAKFlip MX4 vs UnderCover Ultra Flex: which should you buy?](#bakflip-mx4-vs-undercover-ultra-flex-which-should-you-buy) - [FAQ](#faq) ## Before you choose - [The Best Hard Tri-Fold Tonneau Covers of 2026: 6 Hard Folding Covers Compared](https://truckcoverguide.com/posts/best-hard-tri-fold-tonneau-covers/) - [BAKFlip MX4 vs BAK Revolver X4s: Hard Fold or Hard Roll-Up?](https://truckcoverguide.com/posts/bakflip-mx4-vs-revolver-x4s/) - [The Most Secure Tonneau Covers of 2026: Keyed, Hard and Slash-Resistant Picks](https://truckcoverguide.com/posts/most-secure-tonneau-covers/) The BAKFlip MX4 vs UnderCover Ultra Flex decision comes down to a short list of differences, because the two covers are so alike. For most owners we’d buy the [BAKFlip MX4](https://truckcoverguide.com/tonneau-covers/bakflip-mx4/): it publishes a 400 lb rating, has a rack-ready version and has by far the larger owner base. The [UnderCover Ultra Flex](https://truckcoverguide.com/tonneau-covers/undercover-ultra-flex/) is the better choice if you carry tall loads and want to shut the tailgate on them, if you have a Ram with the Multi-Function tailgate, or if it’s cheaper for your truck. Both are hard aluminum folders that stand the folded stack upright behind the cab, both can be driven fully open, and both clamp on without drilling and come with a 5-year warranty. We haven’t tested either one ourselves. This comparison uses the maker copy on Amazon, etrailer’s reproduction of BAK’s spec sheet, owner ratings and the listings we checked on November 12, 2026. Where a figure is a maker claim, we say so. ## Quick comparison | | BAKFlip MX4 | UnderCover Ultra Flex | | --- | --- | --- | | Type | Hard folding, stands upright on prop rods | Hard folding, stands upright on dual prop rods | | Panels | Aluminum over a high-density core, matte | Aluminum, matte black, carpeted underside | | Lock | Auto-latching, secured by tailgate | Secured by tailgate | | Bed access (maker claim) | 100%, drive fully open | 100%, drive closed, partly open or fully open | | Load rating (maker) | 400 lb | Not published | | Sealing | Edge-to-edge rubber seals, drain tubes | Dual-action tailgate seal, up or down | | Weight | Not published | 70 lb (F-150 listing) | | Warranty | 5 years | 5 years | | Made in | USA (per etrailer) | USA with global materials (maker claim) | | Rack version | MX4 TS (T-slot rails) | None confirmed | | F-150 5.5 ft price | $1,199.99 | $1,299.99 | | Our score | 8.2 / 10 | 8.1 / 10 | ## Bed access and everyday use On paper the two are a tie: each says 100% bed access, and each lets you drive with the cover fully open. Our [bed access calculator](https://truckcoverguide.com/tools/bed-access-calculator/) allows about 6 in at the cab for an upright stack on both, which leaves roughly 61 in of the F-150’s 67 in box open. What each cover type leaves usable on a 5.5 ft bed Side view, cab on the left, 67.1 in bed floor (the 2021+ F-150 5.5 ft box). Open bed Covered by the opened cover (low cargo still fits under) Floor taken by a canister Soft roll-up Includes our estimate 88% 4 ft 11 in open-top Hard roll-up Includes our estimate 79% 4 ft 5 in open-top Soft tri-fold, folded From maker/retailer figures 67% 3 ft 9 in open-top Hard tri-fold, folded From maker/retailer figures 67% 3 ft 9 in open-top Hard fold, stood up Includes our estimate 91% 5 ft 1 in open-top Retractable From maker/retailer figures 80% 4 ft 6 in open-top Hinged one-piece From maker/retailer figures Low cargo only close to drive Run your own bed length in the [bed access calculator](https://truckcoverguide.com/tools/bed-access-calculator/). The differences show up in daily use: - **The MX4** folds forward in sections and stands the stack on prop rods. BAK says you can drive fully open. - **The Ultra Flex** stands upright on dual prop rods without resting on the back of the cab, which should spare the cab paint. UnderCover lists three secure positions: closed, partly closed and fully open. - **Tailgate with the cover up.** UnderCover says its dual-action tailgate seal lets you close the tailgate with the cover up or down. That helps if you carry something tall at the front of the bed and want the gate shut behind it. We didn’t find the same claim in BAK’s specs for the MX4. - **Rear window.** Upright panels block it on both covers, so expect to rely on mirrors and the camera. If you rarely haul anything taller than the bed rails, none of this matters. If you do it weekly, the tailgate seal is the one genuine usability edge in this comparison. ## Security and locking Neither cover has a key. The MX4’s patented latches engage automatically as each panel closes, and the Ultra Flex is secured through your tailgate lock. On our three security levels both are level 2: hard panels that stop casual theft, held shut by a locked tailgate. If someone gets the tailgate open, both covers open too. So security is a tie, and the practical fix is the same for both. If your tailgate doesn’t lock, add a [Pop & Lock tailgate lock](https://www.amazon.com/dp/B00TPXG0NO?tag=truckcoverguide.com-20). If tools live in the bed, our [most secure tonneau covers](https://truckcoverguide.com/posts/most-secure-tonneau-covers/) guide covers keyed alternatives. ## Load rating This is the clearest spec gap. etrailer’s copy of BAK’s spec sheet gives the MX4 a 400 lb rating, evenly distributed. The Ultra Flex listing publishes no load rating at all. That doesn’t mean it can’t carry weight, but you have nothing from the maker to rely on, so don’t stack gear or stand on it. Treat either cover as a lid, not a deck. If you need a high rating on the cover, the [Extang Solid Fold ALX](https://truckcoverguide.com/tonneau-covers/extang-solid-fold-alx/) lists 600 lb in our hard-folder roundup. ## Weather sealing We found no published water test, from the makers or independent, for either cover. The MX4 uses edge-to-edge rubber seals and a built-in drainage system with drain tubes, so route the tubes through the bed’s drain holes and keep them clear. The Ultra Flex’s headline sealing feature is the dual-action tailgate seal; the listing gives no more detail than that. The tailgate gap is a common leak point on folders, so a seal designed to work with the cover up or down is a sensible feature, but it isn’t proof the Ultra Flex stays drier. No cover we track is truly waterproof. See [are tonneau covers waterproof?](https://truckcoverguide.com/posts/are-tonneau-covers-waterproof/) for what to expect. ## Installation Both are no-drill, clamp-on installs. BAK claims a one-person install in under 30 minutes for the MX4, which is a maker claim. UnderCover gives no time for the Ultra Flex, and its F-150 listing shows a 70 lb weight, so a second person makes placing it easier. Plan on longer than the claim the first time either way. Hard folders clamp to the exact shape of your rails, so the right part number matters more than the brand. Our [install guide](https://truckcoverguide.com/posts/how-to-install-a-tonneau-cover/) covers squaring the rails and setting the seals. ## Bed racks and accessories BAK sells the MX4 TS, a version with T-slot rails for racks, and etrailer confirms the TruXedo Elevate rack fits the MX4. It also warns that the Thule TracRac SR can interfere with the MX4’s seals. For the Ultra Flex we found no maker-confirmed rack pairing, so this one is a gap if you plan to carry kayaks, ladders or a rooftop tent. More options are in [tonneau covers with a bed rack](https://truckcoverguide.com/posts/tonneau-cover-with-bed-rack/). The Ultra Flex has a carpeted underside, which is a small nicety for cargo that touches the panels from above. Whichever you buy, a bed mat protects the floor, and the [Husky bed mat](https://www.amazon.com/dp/B084J67MZR?tag=truckcoverguide.com-20) suits the F-150 5.5 ft bed. See the [accessories page](https://truckcoverguide.com/accessories/) for more. ## Prices for the same trucks Both are sold per truck and bed, and we only compare listings that fit the same bed. These are the Amazon prices we saw on November 12, 2026: | Truck and bed | MX4 | Ultra Flex | Cheaper | | --- | --- | --- | --- | | Ford F-150 2021+, 5’7” | $1,199.99 | $1,299.99 | MX4 by $100 | | Ford F-150 2021+, 6’7” | $1,271.15 | $1,249.99 | Ultra Flex by about $21 | | Toyota Tacoma 2016–2023, 5’ | $1,277.98 | $1,199.99 | Ultra Flex by about $78 | | Toyota Tundra 2022+, 5’7” | $1,233.73 | $1,249.99 | MX4 by about $16 | | Colorado/Canyon 2023+, 5’2” | $1,220.19 | $1,199.99 | Ultra Flex by about $20 | The “MX4 is $100 cheaper” line is true on the most popular fitment, the F-150 5.5 ft, but it isn’t the pattern across trucks: on three of these five, the Ultra Flex was cheaper. The gaps are small enough that a coupon or a shipping difference could flip them. Prices move often, so check both listings: [MX4 price](https://www.amazon.com/dp/B08L44X6NZ?tag=truckcoverguide.com-20), [Ultra Flex price](https://www.amazon.com/dp/B08L44F1TH?tag=truckcoverguide.com-20). We don’t quote sale prices because we can’t verify them as they change. ## Fitment: which one covers your truck Fitment is where the two diverge most. - **Ram 1500.** The standard MX4 listing (5’7” bed) doesn’t fit the Multi-Function (split) tailgate, and RamBox trucks need the RB version. The Ultra Flex has a 6’4” listing, part UX32013, made for the Multi-Function tailgate (without RamBox). Our [Ram 1500 guide](https://truckcoverguide.com/posts/best-tonneau-cover-for-ram-1500/) walks through the split-tailgate problem. - **Silverado/Sierra.** The MX4 listing we checked is for the 5’10” bed and the Ultra Flex listing is for the 6’7” bed, so they aren’t a like-for-like pair in our data. Both note that they work with MultiPro/Flex tailgates. - **Tacoma, Ranger.** We checked the MX4 for the 2016–2023 and 2024+ Tacoma and for the Ranger, but the Ultra Flex only for the 2016–2023 Tacoma. - **Model years.** The Ultra Flex listings we checked end at 2025, while the MX4’s run to 2027 on most trucks. If you own a 2026 truck, confirm fitment with the listing’s tool before you order. Not sure which bed you have? Use the [bed size finder](https://truckcoverguide.com/tools/bed-size-finder/), then check the part number for your truck against the listing. ## Owner track record The MX4 has the bigger owner base by a wide margin: 763 ratings averaging 4.2 on the F-150 5.5 ft listing, 1,839 on the Silverado listing and 1,285 on the Ram, per the Amazon listings we checked. The Ultra Flex had 46 ratings averaging 4.4 on the F-150 listing and 238 averaging 4.3 on the Silverado listing. A higher average on fewer ratings tells you less, but neither cover shows a red flag. The MX4 has a longer public history, and its newer versions are covered in the [MX4 review](https://truckcoverguide.com/tonneau-covers/bakflip-mx4/). ## Who should skip each one - **Skip the MX4** if closing the tailgate over a tall load is a regular need (UnderCover claims it, BAK’s specs we found don’t), or if your Ram has the Multi-Function tailgate. - **Skip the Ultra Flex** if a published load rating matters, if you plan to put a rack on it or if you want the longest owner record. - **Skip both** if you need a cover that locks with its own key, or if budget is the main concern. The [Gator EFX](https://truckcoverguide.com/tonneau-covers/gator-efx/) costs about half as much and opens about two-thirds of the bed; see [Gator EFX vs BAKFlip G2](https://truckcoverguide.com/posts/gator-efx-vs-bakflip-g2/). ## BAKFlip MX4 vs UnderCover Ultra Flex: which should you buy? - **Most owners:** the MX4. Same warranty and access, a published 400 lb rating, a rack-ready version and the bigger track record. - **You haul tall cargo and want the tailgate shut:** the Ultra Flex, for its dual-action tailgate seal. - **Ram 1500 with the Multi-Function tailgate:** the Ultra Flex 6’4” listing. - **You plan a bed rack:** the MX4 TS. - **Whichever is cheaper for your truck:** on a near-tie like this, price per fitment should break it. Still weighing hard folders against other designs? Our [best hard tri-fold tonneau covers](https://truckcoverguide.com/posts/best-hard-tri-fold-tonneau-covers/) ranks every folder we track, and [BAKFlip MX4 vs Revolver X4s](https://truckcoverguide.com/posts/bakflip-mx4-vs-revolver-x4s/) compares the MX4 with BAK’s hard roll-up. For F-150 owners, [the best tonneau cover for the F-150](https://truckcoverguide.com/posts/best-tonneau-cover-for-f150/) covers fitment details, and the [cover matcher](https://truckcoverguide.com/tools/cover-matcher/) ranks every line we track against how you use your bed. ## Don't guess. Calculate. - [📏 Bed Size Finder](https://truckcoverguide.com/tools/bed-size-finder/): what bed length your truck has - [🎯 Cover Matcher](https://truckcoverguide.com/tools/cover-matcher/): which cover type suits you - [📐 Bed Access Calculator](https://truckcoverguide.com/tools/bed-access-calculator/): usable bed with the cover open - [📊 Compare every cover](https://truckcoverguide.com/tonneau-covers/): sortable spec table ## Frequently asked questions ### Is the BAKFlip MX4 or the UnderCover Ultra Flex better? For most owners the MX4: it publishes a 400 lb load rating, has a T-slot version for racks, has thousands of owner ratings and costs about $100 less on the 2021+ F-150 5.5 ft. Choose the Ultra Flex if you carry tall loads and want to shut the tailgate with the cover up, if you have a Ram with the Multi-Function tailgate, or if it's cheaper for your truck. ### Can you close the tailgate with the BAKFlip MX4 or Ultra Flex open? UnderCover says the Ultra Flex's dual-action tailgate seal lets you close the tailgate with the cover up or down. BAK's specs that we found don't make that claim for the MX4, so don't assume it. Check BAK's instructions if shutting the gate on tall cargo matters to you. ### Which is more secure, the MX4 or the Ultra Flex? They're equal on our scale. Both have hard aluminum panels, both are secured by your locked tailgate and neither has a key of its own, so each is level 2 of 3. If the tailgate opens, the cover opens too. For a keyed cover, look at the UnderCover Elite or RetraxPRO MX. ### Which has the better warranty? They match: both carry a 5-year warranty according to the maker copy we checked. UnderCover also sells a cheaper Flex with a 3-year warranty and an Armor Flex with LINE-X coated panels. ### Do the MX4 and Ultra Flex fit a Ram with the Multi-Function tailgate? The standard BAKFlip MX4 listing for the 2019+ Ram 1500 5'7" bed doesn't fit the Multi-Function (split) tailgate. The UnderCover Ultra Flex has a 6'4" listing (part UX32013) made for it, without RamBox. Always confirm with the listing's fitment tool. ### Can you put a bed rack on the MX4 or Ultra Flex? BAK sells an MX4 TS with T-slot rails for racks, and etrailer confirms the TruXedo Elevate rack fits the MX4. We found no maker-confirmed rack pairing for the Ultra Flex, so ask UnderCover or the rack maker before you buy. ## Sources - [Amazon: BAKFlip MX4 for the 2021–2027 F-150 5'7" bed (448339)](https://www.amazon.com/dp/B08L44X6NZ?tag=truckcoverguide.com-20) · checked 2026-11-12 — $1,199.99 with 763 ratings averaging 4.2 when checked. - [etrailer: BAKFlip MX4 (Ram 1500 2019+ 5'7") specs and Q&A](https://www.etrailer.com/Tonneau-Cover/BAK-Industries/BAK448227.html) · checked 2026-11-12 — 400 lb evenly distributed, drain tubes, 5-year warranty, made in USA; TruXedo Elevate rack confirmed, Thule TracRac SR can interfere with the seals. - [Amazon: UnderCover Ultra Flex for 2021–2025 Ford F-150 5'7" bed (UX22029)](https://www.amazon.com/dp/B08L44F1TH?tag=truckcoverguide.com-20) · checked 2026-11-12 — Drive closed, partly open or fully open; folds upright on dual prop rods without resting on the cab; 5-year warranty. - [Amazon: UnderCover Ultra Flex for 2019–2025 Ram 1500 6'4" bed with Multi-Function tailgate (UX32013)](https://www.amazon.com/dp/B0BYPJ1B5D?tag=truckcoverguide.com-20) · checked 2026-11-12 — $1,349.99; made for trucks with the Multi-Function tailgate, without RamBox. ## Get new guides by e-mail One short e-mail when Truck Cover Guide publishes a new guide. No spam, no sharing your address, and you can unsubscribe in one click. E-mail address New posts only · Unsubscribe anytime · [Privacy](https://truckcoverguide.com/privacy/) Our #1 pick Best for most owners: 400 lb rating, biggest owner base, about $1,200 for the F-150 5.5 ft ![BAKFlip MX4 Hard Folding Tonneau Cover](https://truckcoverguide.com/_astro/bakflip-mx4.CoOqV3JL_ZwWQMx.webp) ### [BAKFlip MX4 Hard Folding Tonneau Cover](https://truckcoverguide.com/tonneau-covers/bakflip-mx4/) 8.2 - Hard folding - Aluminum panels - 100% bed access Most truck owners who want a lockable hard cover that still opens the whole bed and has the longest owner track record of any hard folder. $$$$ Premium Price tier: Premium F-150 5.5 ft listing on Amazon [Check price on Amazon](https://www.amazon.com/dp/B08L44X6NZ?tag=truckcoverguide.com-20)[Read the full review](https://truckcoverguide.com/tonneau-covers/bakflip-mx4/) [📏 Which bed do you have? Make, model, year and cab in; bed length out, from the maker's spec sheet.](https://truckcoverguide.com/tools/bed-size-finder/)[🎯 Roll-up, fold or retractable? Match a cover type to your security, access and budget in 30 seconds.](https://truckcoverguide.com/tools/cover-matcher/) ## Keep reading [Hard folding ### The Best Hard Tri-Fold Tonneau Covers of 2026: 6 Hard Folding Covers Compared The best hard tri-fold and hard folding tonneau covers of 2026: BAKFlip MX4, Gator EFX, UnderCover Ultra Flex, Extang Solid Fold ALX and more, with prices. Updated Nov 12, 2026](https://truckcoverguide.com/posts/best-hard-tri-fold-tonneau-covers/)[Head-to-head ### BAKFlip MX4 vs BAK Revolver X4s: Hard Fold or Hard Roll-Up? BAKFlip MX4 vs BAK Revolver X4s: hard folding vs hard roll-up compared on access, security, sealing, install, racks and verified prices for the same trucks. Updated Nov 12, 2026](https://truckcoverguide.com/posts/bakflip-mx4-vs-revolver-x4s/)[Security ### The Most Secure Tonneau Covers of 2026: Keyed, Hard and Slash-Resistant Picks The most secure, best locking tonneau covers of 2026: keyed retractables, one-piece lids and slash-resistant roll-ups, plus how our three security levels work. Updated Nov 12, 2026](https://truckcoverguide.com/posts/most-secure-tonneau-covers/) Best for most owners: 400 lb rating, biggest owner base, about $1,200 for the F-150 5.5 ft BAKFlip MX4 $$$$ Premium Price tier: Premium [Check price](https://www.amazon.com/dp/B08L44X6NZ?tag=truckcoverguide.com-20)