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The flippable Plank Firm is unlike any hard bed I’ve tested — it’s ultra-supportive yet so comfy. Here’s why it’s still the best firm mattress online
I first tested the Plank Firm mattress in a showroom in Arizona, where the exceptional hardness of this double-sided all-foam bed stood out in a sea of medium-firm comfort. As a stomach sleeper and firm mattress fan, I knew I had to test it and see how it compares to the best mattresses you can buy online.
The Plank Firm, which is down to $999 from $1,332 for a queen at Plank, promises to be the firmest mattress on the market. Right from the first night I recognized that the hard support could work wonders for easing my back pain — and horrify those who prefer a marshmallow soft bed.
My 2-minute review of the Plank Firm mattress
- The Plank Firm is a true firm mattress, with a hard and even support across the body to hold the spine lifted and aligned.
- It's also a flippable mattress with two sides to choose from. The Firm side is the crowd-pleaser with a touch more cushioning while the Extra Firm is for those who crave unyielding support.
- Edge to edge support means the side and corners as strong as the center of the bed. That's good news if you want to stretch out and indicates a durable build.
- It's too firm for most side sleepers. I could enjoy a few nights lying on my side but the lack of cushioning is likely to lead to sore shoulders and hips.
My Plank Firm Mattress review took place over two months, during which I spent at least three weeks sleeping on each side of this flippable bed. It takes three weeks to break a mattress in and this adjustment period was necessary because even as a firm bed connoisseur, I was taken aback by the Plank.
A double-sided bed that can be flipped between a 'Firm' and 'Extra Firm' feel, the Plank mattress has almost no sink. It holds your body aloft from head to toe, ensuring your feet, knees, hips, shoulders and neck are all in alignment.
I've been struggling to describe the feel of the Plank Firm, particularly the Extra Firm side. "Very firm foam" is obvious but uninspired, "a hardwood floor with a luxurious carpet" is another, and my colleague Nicola's description of "soft grass" is surprisingly accurate. I say it's a bit like stale pound cake — hard but with an echo of squishiness. I mean that as a compliment
While the other firm beds I've tested, including the Helix Dawn and the Siena Signature mattress, have some contouring, the Plank barely gives way even beneath the heaviest parts of my body.
As a result, lying on my back or stomach results in no strain at the lumbar — that's the 'S' part of my lower back, an area prone to sinking when sleeping on a mattress that's too unsupportive. This is why it's among the best mattresses for stomach sleepers: it supports the spine even in prone position.
A flippable bed with an uber-firm build could be a gimmick but the Plank Firm mattress backs up its unusual design choices with exceptional support and a quality finish
On my side, however, a problem appears. With minimal comfort layers, your shoulder and hips press hard into the mattress, most noticeably on the Extra Firm feel. For lightweight side sleepers, your arm will likely start to protest in minutes (my colleague Frances Daniels matches this description and could barely last 10 minutes on the Plank.)
The very hard feel has a few other consequences. The motion isolation is excellent as the deadened foams absorb all your partner's wriggling, while the strong edges mean you can stretch out happily.
A flippable bed with an uber-firm build could be a gimmick but the Plank Firm mattress backs up its unusual design choices with exceptional support and a quality finish. After testing it I recommend the Plank to stomach sleepers and back sleepers who want to avoid excess softness.
What I like about the Plank Firm mattress
It's a true firm mattress
The Plank mattress is a dual-sided bed but don't worry; you can expect a hard feel both ways up. While there is a notable difference between the sides, the shared 'high-density support foam' core delivers a base level of firmness that defines the Plank.
Let's start with the Firm side, as this is the biggest crowd pleaser. Featuring two-inches of comfort foam on top of that support core, I rate it an 8 out of 10 on the mattress firmness scale. It gently contours to the hips and shoulders but the quilted surface has no 'sink' — it bounces back the instant pressure is removed.
The Extra Firm side takes the hardness up a notch; I rate it 9 out of 10. When I placed a 25kg weight on top of the bed it hardly sank at all — it was like putting it on a table. But as this is foam, there's an inherent squishiness that gives the Plank mattress just enough cushioning to keep you comfortable.
It's the kind of performance I expect from a firm mattress but rarely get. If you've been disappointed by the light touch of other firm beds, trust the Plank to live up to its name.
It's flippable
I'll admit I was a sceptic of double-sided beds but the Plank Firm mattress won me over because I could see the benefits to both sides. What's more, I flipped the bed over even when I wasn't required to do so for my review. As someone who hates extra effort at bedtime, this is a strong endorsement.
The two sides of the Plank Mattress share similar DNA while providing different benefits. Both sides are hard — which appeals to me as a firm mattress lover — but one side has cushioned bounce while the other has flat support.
So on nights where I need more support at the lower back (perhaps too much hunching over my laptop), I'll opt for the Extra Firm. When I want more cushioning (maybe a sore elbow or knee), I'll go Firm.
And if you're an occasional bed sharer, I can see the benefits as well. The Firm is more of an all-rounder, so likely better when there's two. Then you can switch to Extra Firm when you have the bed to yourself.
It's ultra-supportive
The Plank Firm mattress doesn't compromise when it comes to support. Flipped either way, your body is lifted and aligned with no dipping or sagging. As a stomach sleeper, this is just what I look for in a bed — support that keeps my hips lifted and in a line with my spine.
Mattress tester Alison Barretta also tried the Plank in Arizona and loved the Firm feel on her back. She experiences mild scoliosis and said the cushioning perfectly filled the gap between the spine and her bed, reducing strain.
And the support doesn't let up, even at the edges. I could sit or lie right on the sides of the mattress and feel just as supported as I did at the center.
This is a plus for solo sleepers (hello, starfishing!), couples (you can both spread out) and those who like to lean on the bed when getting up in the morning. Press all your weight on the sides of the Plank Firm and the edge support will have your back.
It's durable
The Plank mattress has a relatively simple build that primarily consists of a six-inch 'high density' support foam core with a bit of padding on either side.
Just from lying on the mattress you can feel the quality of the foam. Neither me nor my cast iron weight made much of a dent in the surface and during the testing period I didn't notice any sagging or sinking.
I'd also note that the Plank can support up to 950lbs — that's the weight range of the best mattresses for heavy people and suggests good durability.
And with two sides to sleep on, the Plank Firm has double the materials to wear out. So when one side looks tired, the other can take over.
Plank offers a limited lifetime warranty, which speaks to the expected durability of the mattress (although the warranty doesn't protect against usual wear and tear.)
What I don't like about the Plank Firm mattress
It's too firm for most side sleepers
The best mattresses for side sleepers are typically defined by their cushioning. For example, the CopperFlex Pro Hybrid (from Brooklyn Bedding, the same brand behind the Plank) uses a thick Euro top to relieve pressure at the shoulders and hips.
But the Plank lacks nearly all cushioning, particularly the Extra Firm side which has just .75 inch of quilting between your body and the support core. As a result, side sleepers are likely to find their hips, knees and shoulders are sore by the morning.
The Firm side is a little better. Two inches of comfort foam make it suitable for some combination sleepers and side sleepers with a heavier build.
And it's not just side sleepers who might find themselves at odds with the Plank mattress. The firm feel can be too hard for back sleepers, leading to pressure build up at the shoulders.
It can sleep hot
I was expecting the Plank Firm to be a relatively cool-sleeping mattress. After all, with almost no sink there's less opportunity for warmth to become trapped between you and the bed.
However, the exceptionally dense foams of the Plank mattress do tend to hold onto heat, leading to some nights when I woke up sweating.
This isn't unusual for an all-foam beds — even the best memory foam mattresses can struggle with temperature regulation — but it might cause some issues for hot sleepers.
However, Plank does offer a solution. A GlacioTex cooling cover is available for around $150 extra and should improve the cooling.
It doesn't come with handles
On most mattresses a lack of handles is a minor annoyance (be honest, how often do you actually move your mattress?)
On the Plank Firm, a bed that's designed to be regularly flipped, missing handles seem like an oversight.
I could flip my full-size mattress by myself but I would have appreciated something to hold onto once I'd got to the 90° angle. For a queen or above, you're likely to need a helping hand, particularly as with no handles it's hard to get a grip on the bed.
Who I recommend the Plank Firm mattress to
✅ Stomach sleepers: Stomach sleepers like myself will benefit from the even firmness of the Plank mattress; I felt like it straightened me out after a day of hunching. Many back sleepers will enjoy the same benefit.
✅ People with back pain: The next-level support of the Plank can help prevent your back from sagging or twisting (although as I'll explain below, firm mattresses aren't right for every type of back pain.)
✅ Anyone who has been disappointed by firm mattresses: Some beds promise firm but fall flat on delivery. The Plank lives up to its name as a bed that's as hard as a Plank (but still comfortable.)
Who I don't recommend the Plank Firm Mattress to
❌ Side sleepers: There are some side sleepers who'll like the Plank Firm, including those of a heavier build, but for the most part his ultra-firm mattress lacks the cushioning you need at the shoulders.
❌ Very hot sleepers: With a tendency to trap heat within the dense foams,. the Plank can cause some night sweats. Unless you're willing to pay for the GlacioTex cover, of course.
❌ Anyone looking for a traditional foam feel: You might be tempted to see the all-foam interior of the Plank and expect a marshmallow mattress — you'll be very disappointed. The Nectar Premier Memory Foam Mattress is a more cushioned alternative (and I've tested them both.)
What to look for in a firm mattress
I've tested a variety of firm mattresses and the first thing I look for is even, reliable support. Lying back, you should feel held aloft from head to toe, with no sinkage at the hips or shoulders. You can test this by lying on the mattress and assessing your body for signs of strain.
I also employ a low-tech 'press' test — how easy is it to press my hands into the surface? If the materials yield easily, the mattress might feel firm at first but is likely to soften during the night. A true firm mattress won't cave to pressure.
And don't forget to test the sides; weak edges suggest the firmness peters out at the perimeter, indicating future sagging. We use a weight as part of the mattress testing process but sitting on the sides is a good at-home test.
Firmness might be your focus but cushioning matters too and there should be at least a comfort layer between you and the support core to ensure pressure relief (on the Plank's Extra Firm side, that's the quilted top.)
When shopping online, pay close attention to the mattress firmness. This is usually a scale of 1-10, with 10 indicating rock hard and one marshmallow soft. Firm mattresses tend to sit at the 7.5-10 mark but some brands using their own system, so read the scale closely.
And always, always look for a mattress trial. Firmness is subjective and a trial gives you a chance to decide if the feel is right for you. The Plank Firm mattress trial is 120 nights.
Are firm mattresses good or bad for back pain?
Firm mattresses are often recommended for those with back pain as the stable support can help with spinal alignment. On that note, orthopedic mattresses tend to sit at the firmer end of the scale.
Speaking to us about the benefits of firm mattresses for back pain, sleep expert Dr. Mark Aloia explained that firm mattresses can help relieve strain at the shoulders and lumbar.
"The idea that a hard mattress is good for back pain is a concept that has been reinforced over time by medical advice and cultural practices," he added. "We can tell by looking at spinal alignment that a firmer bed can help in that area."
However, as Dr. Aloia noted, back pain is "highly variable", making it difficult to recommend a specific mattress firmness for back pain.
Lightweight sleepers and side sleepers with back pain are typically better with a medium-firm mattress, which offers support as well as pressure relief.
In our guide to the best mattresses for back pain, you'll find a variety of firmnesses, to better target the individual comfort needs.
Do firm mattresses last longer than soft or medium mattresses?
Firm mattresses often last longer than soft and medium mattresses because the dense foams are designed not to give way under pressure. With less stress from contouring to the body and bouncing back, they're slower to sag.
However, feel is just one part of the equation when it comes to durability. Material quality is important and high density foams have better longevity overall. Density refers to the amount of foam per inch and it doesn't indicate feel — both firm and soft foams can be high density.
As a general rule, the average mattress lasts six to 10 years, with foam beds tending to last longer than hybrids (no springs to break.) Latex mattresses often have the best durability of all and as an added bonus, tend to have a firmer feel as well.
