Helix Dawn vs Plank Firm: which firm mattress should you buy?

It's the battle of the firm mattresses, as we pit the Helix Dawn and Plank Firm against each other. If you need the enhanced support of a firm bed, this guide explores if the Helix Dawn or Plank Firm mattress is right for you.

Our sleep experts have spent combined months sleeping on the Helix Dawn and Plank Firm and we rate them among the best mattresses we've tested. As well as a firm feel, the two share a mid-range price point and a supportive build that suits back and stomach sleepers.

Here we're comparing the support, comfort and price of the Helix Dawn and Plank Firm mattresses to help you decide which of our favorite firm mattresses suits your sleep needs.

Helix Dawn vs Plank Firm mattress: Overview

It's a close head to head between the Helix Dawn and Plank, with both ranking among the best mattresses in a box we've tested. Below, we'll give a full rundown of how these mattresses stack up but here's a quick overview.

The Dawn is a hybrid design and like the best hybrid mattresses we've tested it delivers support via its spring base.

In our Helix Dawn Mattress review we praised its gentle contouring and responsive feel: our tester could move around without losing support (not that they needed to toss and turn to get comfortable.)

The Plank Firm is an all-foam mattress and without any springs, it uses a dense foam core for firm support all-round. It's just as firm as you expect from a bed named the 'plank'. Particularly on the Extra Firm side because did we mention? It's a double sided mattress.

Firm on one side, Extra Firm on the other, we liked both in our Plank Firm Mattress review but while the Firm side is the crowd pleaser, the niche appeal of the Extra Firm impressed our testers.

Helix Dawn vs Plank Firm mattress: Price & trial

• Both are mid-range mattresses in the year-round sales
• Helix Dawn has a 100-night trial, Plank a 120-night trial
• Both come with a lifetime warranty

The Helix Dawn and Plank Firm Mattress are mid-range mattresses and cost around $1,000 for a queen. The Helix Dawn is slightly pricier with a queen $1,099 in the standard Helix Mattress sale but as a queen Plank Firm typically sells for $999, there's not much in it.

Both brands offer deals throughout the year — look out for 20% off at Helix and 25% off at Plank — but good timing can help you save more. Around peak sales days, such as Black Friday and Memorial Day, Helix has a tendency to boost the sale to 25%, while Plank offers 30% off on special occasions.

The DreamCloud Premier mattress and the CopperFlex Hybrid Pro mattress also fit in this price range. We think the Dawn and Plank offer competitive value.

You get a limited lifetime warranty with both the Helix Dawn and Plank but the Plank does have a slightly better trial period: 120 nights, compared to 100. However, it's worth remembering the Plank is a double-sided mattress, so you almost have two beds to test out during that sleep trial.

Helix Dawn Mattress: twin was $998.66 now $729.03 at Helix Sleep
You can always save 20% at Helix but right now is the time to buy as you can score 27% off with our code TOMS27. This reduces a queen from $1,332 to $972 which is the best mattress sale we think you're going to get.

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Plank Firm Mattress: twin was $749 now $561.75 at Plank
As a double-sided and extra firm mattress, the Plank Firm is a niche entry to the sleep market and we think the mid-range price is a good deal. In the standard sale a queen is $999 (was $1,332). We have seen 30% off in recent weeks reducing a queen to $932 but we think it might be a while before that deal reappears.

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Helix Dawn vs Plank Firm mattress: Design

• Helix Dawn is a hybrid mattress with a spring base and firm foams
• Plank Firm is a dual-sided memory foam mattress
• Both have cooling add-ons, Dawn also has a support upgrade

The Helix Dawn and Plank Firm mattresses share a firm feel and we'll explore what that's like to sleep on below. For now, we're focusing on how they achieve this firmness. When it comes to design, these mattresses couldn't be more different.

To be fair, the Plank Firm is different to most mattresses. While we rank it among the best memory foam mattresses we've tested, it doesn't have the traditional build we'd expect from an all-foam bed.

First, it's double-sided. Flipped one way, the Plank is Firm. Flipped the other, it's Extra Firm.

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To create this, the Plank Firm features a dense six-inch support core that sits in the middle of the mattress. This is largely responsible for the feel of the mattress and on the Extra firm side, it's topped only by .75" of foam.

On the Firm side there's a bit more padding: two more inches of foam, plus the .75" of the quilted cover.

The Helix Dawn is a hybrid mattress and unlike the Plank, it sticks to tradition. Four foam layers, including a layer of latex-alternative dynamic foam and two layers of firm response foam, sit on top of a spring base with a final layer of base foam for durability.

Helix Dawn vs Plank Firm mattress: Comfort & support

• The Plank Extra Firm side is the firmest mattress we've tested
• The Plank Firm side and Helix Dawn have a comparable firm feel
• Both best suit back and stomach sleepers

We've tested both the Helix Dawn and Plank Firm mattresses and we consider them among the best mattresses for stomach sleepers you can buy online.

Mattresses for stomach sleepers are typically firm with plenty of support. Stomach sleeping places the back at an awkward angle but a firm mattress keeps the spine straight to limit twisting and prevent pain.

The Helix Dawn is a classic stomach sleeper mattress: firm with ample support from a spring base. Our testers agreed it was an 8 out of 10 on the mattress firmness scale, 10 indicating rock hard.

We found the upper foam layers contoured gently around the body to prevent pressure build up, impressing our back sleeping testers.

Side sleeping was also comfortable on the Dawn, mostly in short bursts. Dedicated side sleepers should consider a softer mattress, such as the Helix Midnight Mattress, which has more cushioning at the shoulders.

Our lead tester spent multiple weeks sleeping on both sides of the Plank Firm to build up a full picture of the comfort. Across our testing panel, one thing immediately stood out when lying on the Extra Firm side: it's really firm.

While it shouldn't be a surprise, we were taken aback by the hard feel, rating it 9 out of 10. But it took only a few minutes for the back and stomach sleepers to appreciate how supportive it is.

Side sleepers, however, should avoid the Extra Firm side. There's not enough cushioning at the pressure points, resulting in aching arms and hips.

The Firm side does have more cushioning, partly due to the added foam but also because the looser quilting gives more bounce to sink into. This side is better for side sleepers although as with the Dawn, mostly in short bursts.

Like the Dawn, we rated the Firm side 8 out of 10 for firmness. Our lead tester is a stomach sleeper and while she loved the Extra Firm side sometimes it pressed too hard against the stomach. For example, after a late dinner.

The Extra Firm side divided our testers with some (primarily the side sleepers) unable to find comfort. The Firm is more of a crowd pleaser.

Helix Dawn vs Plank Firm mattress: Performance

• Plank can trap some heat, both have cooling add-ons available
• Dawn has strong sides but the Plank's edge support is exceptional
• Good motion isolation overall, Plank just comes out on top

Overheating can disrupt sleep but for the most part, both the Dawn and the Plank remain a neutral temperature overnight. Our testers did feel the beds could, on warm nights, trap some heat, with the problem more pronounced in the Plank Firm.

We think this will only impact hot sleepers and both Helix and Plank offer a GlacioTex cover upgrade. GlacioTex is used in many top cooling mattresses so we recommend the add-on if you experience night sweats or hot flashes.

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Hybrid mattresses tend to have better edge support than their all-foam equivalents and with reinforced springs on the lengthwise sides, the Helix Dawn is sturdy at the edges (if a little weak at the corners.)

The Plank, however, surprised us with its firm feel from corner to corner: we awarded edge support full marks.

Both mattresses also have good motion isolation, although the Plank just takes the win (those thick foams deaden movement.) But if you share a bed, both mattresses should minimize disruption from a restless partner.

Helix Dawn vs Plank Firm mattress: which should you buy?

Buy the Helix Dawn Mattress if...

✅ You prefer a traditional feel: With tall springs and a bouncy response foam, the Helix Dawn moves when you move for consistent support and comfort. A more traditional innerspring feel than the all-foam Plank.

✅ You want to customize the bed: The Helix Dawn comes with optional cooling and support add ons, plus Helix Luxe and Elite upgrades. The Plank Firm does have some optional upgrades but not as many as the Dawn. (You can see how the Dawn performs against an upgraded model in our Helix Dawn vs Dusk Luxe mattress head to head.)

✅ You're a combination sleeper: We found the Dawn comfortable in most sleep positions, even if dedicated side sleepers might want a few more layers of cushioning, making it a good choice for those who move around in the night.

Buy the Plank Firm Mattress if...

✅ You can never find a firm mattress that's firm enough: If you like the feel of Japanese floor mattresses and find standard beds never provide the support you need, the Plank Firm delivers reliable, consistent firmness.

✅ Your comfort needs change: Double sided mattresses, like the Plank, are best for those who need different support levels on different nights. For example, those with reoccurring injuries or occasional bed sharers.

✅ You like the added support of strong edges: The Dawn has good edge support but the Plank Firm is exceptional. You can sit and press against the side of the mattress without it sinking beneath you, making it easier to get in and out of bed.