Plank Firm vs Siena Mattress: which firm memory foam mattress should you buy?

Memory foam mattresses are best known for their cushioned and cozy feel, but the Plank Firm and Siena Mattress prove the diversity of this popular bed material. These firm memory foam mattresses prioritize support over padding, but which is better?

You'll find both the Plank Firm and the Siena in our guide to this year's best mattresses for all sleepers, and our experienced testing panel was impressed with the edge support and firm feel of the two.

However, the dual-sided design of the Plank Firm and the budget-friendly build of the Siena means there are some key differences between two of the best memory foam mattresses we've reviewed. Read on to discover if the Plank Firm or the Siena Memory Foam Mattress is right for you...

Plank Firm vs Siena Mattress: price & trial

• Plank Firm is mid-range with a 120-night trial and 10-year warranty
• Siena is budget mattress with a 180-night trial and 10-year warranty
• Both brands offer evergreen sales

An evergreen 25% off mattress sale keeps the Plank Firm in the mid-range price bracket. A queen will generally set you back $999, reduced from an MSRP of $1,332. For major sales days (and other celebrations), you'll find 30% off the Plank – this is the best saving we've ever spotted on this mattress.

But when it comes to pricing, the Siena Memory Foam Mattress comes out on top. An evergreen up to 50% off sale reduces a queen to just $399 (was $769). We think it's the best cheap mattress around and it's excellent value for money.

The Siena deal rarely changes, although we have spotted a queen on sale for only $379 before. But for the most part, Siena tends to keep the deals the same, regardless of the occasion.

Despite being the cheaper mattress, Siena offers better benefits. You'll get a 180-night sleep trial at Siena, compared to just 120-nights to test the Plank Firm. Both offer a 10-year warranty, which is the industry average.

Plank Firm vs Siena Mattress: materials & design

• Both the Siena and Plank Firm are all-foam mattresses
• Plank Firm is double-sided, with a Firm and Extra Firm side
• Siena is a simple design with two foam layers

The Plank Firm is the more complex design of the two, which is expected as it's a dual-sided mattress. In the center of the Plank Firm are six inches of incredibly dense support foam. It's this foam that pretty much dictates the overall feel of the Plank Firm.

On one side, the mattress is Firm, on the other, Extra Firm. On the Firm side, the dense middle layer is topped by two inches of comfort foam and a .75-inch quilted top. On the Extra Firm side, there's just a .75-inch quilted top between you and the support foam.

The Siena has a simpler build, consisting of just two foam layers. At the base is an 8.25-inch firm foundational foam layer, topped by 1.75 inches of responsive gel memory foam. It's finished with a soft and breathable cover, with a shift-resistant lower cover to keep things in place.

Both mattresses are vacuum packed, rolled, and delivered in a box. You can expect some mild off-gassing from the Siena, while the Plank had a stronger smell that lingered for a while. However, that's not unusual from even the best mattresses in a box.

Plank Firm vs Siena Mattress: comfort & support

• Plank Firm has a firm feel with limited sink on both sides
• Siena has an initial squishiness on top of a firmer support
• Both are best for stomach and back sleepers

The Plank Firm and Siena are two of the best firm mattresses we've tested, so let's explore what that means. We rank mattress firmness on a scale of one to 10, with one indicating super soft and 10 rock hard. A firm mattress generally fits in the 8-10 bracket.

In our Plank Firm mattress review, we rated this double-sided mattress as an eight of 10 on the Firm side and nine on the Extra Firm side. The unyielding surface is firm from the get-go whichever way you flip it, softening up slightly the more you lie on it.

This gives the Plank Firm a 'lifted' feel. You don't just lie on top of the mattress, you almost feel pushed up by it. This is particularly prominent on the Extra Firm side, as the diamond quilting provides a tight, flat surface. On the Firm side, the jump and track quilting gives some slight padding.

The Siena is also incredibly firm – we rated it nine out of 10 in our Siena Memory Foam Mattress review. However, the Siena does have slightly more of that traditional sink. But once you've got past the initial cushioning, the firmness comes through.

Foam mattresses are generally known for their 'hug' effect, as the material contours to the body. But you won't get much of that with either of these models. That means we don't recommend the Plank or Siena for side sleepers; the best mattresses for side sleepers have more cushioning to relieve pressure around the hips, shoulders and knees.

However, we do recommend the Plank Firm and Siena for back and front sleepers. Our back sleeping testers appreciated the incredible lumbar support of the Extra Firm Plank, while we described the Siena as offering "balanced, full-body support" for back sleepers.

The best mattresses for stomach sleepers are typically firm (to prevent the hips from sinking in), and the sturdy support of the Plank Firm and Siena can help front sleepers stay comfortably aligned throughout the night.

Both mattresses offer good motion isolation, so we would recommend them for couples. The foams absorb your partner's tossing and turning so you won't be woken up in the night. They also both have good edge support, although the Plank Firm does beat the Siena — the Plank Firm is incredibly strong all across the perimeter, and we felt comfortable sitting and sleeping right up to the side.

Plank Firm vs Siena Mattress: temperature regulation

• Plank Firm sleeps slightly warm but you can add a cooling cover
• Siena Mattress has a neutral sleep feel
• The Siena is better for hot sleepers

The Siena impressed us with its temperature regulation. While memory foam mattresses can sleep hot, the lack of sink prevents warmth from being trapped, meaning you're less likely to wake up sweaty.

We expected something similar from the Plank Firm, but in contrast, the dense foams do hold onto some heat. This wasn't a major issue for our testing panel, but if you sleep hot, you might want to upgrade to the GlacioTex cover – this breathable fabric has a cool-to-the-touch feel (but it will cost you roughly an extra $100.)

However, neither mattress can offer the same all-night temperature control of the best cooling mattresses. If you're after a cooling all-foam mattress that isn't too soft, check out our Cocoon by Sealy Chill mattress review.

Plank Firm vs Siena Mattress: which should you buy?

Buy the Plank Firm Mattress if...

✅ You want sturdy edges: The Plank Firm feels as strong at the corner and sides as it does at the center. If you need to push against the mattress to get up in the morning, the Plank will provide a super stable base.

✅ You have changing sleep needs: Want more support? Go for the Extra Firm side. Need cushioning? Switch to Firm. The dual-design gives versatility for people with changing needs, such as those with reoccurring injuries.

✅ You like to feel lifted by the mattress: It's not just that you don't sink into the Plank Firm, the dense foams almost push against you, lifting the body to maintain neutral alignment from the shoulders down.

Buy the Siena Memory Foam Mattress if...

✅ You're on a budget: The Siena is one of the best value mattresses we've tested and it's significantly cheaper than the Plank Firm. We think it's one of the best budget mattresses around.

✅ You want a more traditional foam feel: While the Siena doesn't have the gooey foam feel of something like the Tempur-Cloud (or even the contouring of the Nectar Classic), it does have more sink than the Plank.

✅ You sleep hot: Very hot sleepers should try a dedicated cooling mattress, but between the Plank Firm and the Siena, the Siena sleeps cooler.