Amerisleep AS3 vs Casper The One (2026): Which Wins?

The Amerisleep AS3 is the stronger mattress for most buyers in this comparison. It delivers better motion isolation, a thicker 12-inch profile, a plant-based Bio-Pur build, and a 20-year warranty that is twice as long as Casper's 10-year coverage. The Casper The One has a legitimate case for back and stomach sleepers who prefer a firmer surface: it sits at medium-firm rather than medium, Consumer Reports rated it a top all-foam pick in 2025, and its $799 to $999 queen price makes it $200 to $300 less expensive than the AS3. If you share a bed, sleep on your side, or want the lowest-tox foam build on this list, the AS3 is the clear choice. If you sleep on your back, sleep alone, and want to spend less, the Casper The One is a respectable alternative.

Spec	Amerisleep AS3	Casper The One
Price (queen)	From $1,049	$799-$999
Construction	All-foam (plant-based Bio-Pur)	All-foam (Breathe Flex + Align memory foam)
Firmness	Medium (5/10)	Medium-Firm (6-6.5/10)
Height	12"	11"
Cooling	8.6/10 (open-cell Bio-Pur foam)	8.2/10 (open-cell Breathe Flex top layer)
Motion isolation	9.4/10	8.6/10
Edge support	7.4/10	7.2/10
Trial period	100 nights	100 nights
Warranty	20 years	10 years
Fire barrier	Silica-based (no loose detachable fiberglass), CertiPUR-US	Fiberglass-free (confirmed by Casper)
Made in USA	Yes	Yes (designed and assembled)

Amerisleep AS3 vs Casper The One: Full Comparison

Construction and Materials

The AS3 is a 12-inch mattress built around Amerisleep's Bio-Pur foam, a plant-based polyurethane that replaces a portion of petroleum feedstock with castor oil. The substitution produces a more open cell structure than conventional memory foam, which means air moves through the material more freely. Below the Bio-Pur comfort layer sits the HIVE transition layer, a 2-inch piece of foam with thousands of hexagonal cutouts engineered to vary in firmness by body zone. The cutouts are wider under the shoulders to allow compression, narrower under the hips and lumbar to resist sinking. A high-density polyurethane base provides the structural foundation.

The Casper The One uses three foam layers in an 11-inch profile. The top layer is Casper's Breathe Flex polyurethane foam, an open-cell material designed for airflow and surface responsiveness. Below it sits Align memory foam, a traditional slow-rebound foam that adds contouring and smooths the feel between the top layer and the denser base. The bottom is Casper's Core Continuous Support high-density polyurethane base foam. Casper has confirmed that The One uses no fiberglass as a fire barrier, and it is designed and assembled in the United States within the Carpenter Co manufacturing family. The AS3 uses a silica-based fire barrier rather than loose fiberglass and is CertiPUR-US certified for content and emissions.

The AS3's build is more sophisticated in terms of zoned support and plant-based composition. The Casper The One is a straightforward three-layer foam stack aimed at broad compatibility at a lower price point. Both are CertiPUR-US certified, and neither uses loose detachable fiberglass in its fire barrier.

Firmness and Feel

The AS3 sits at medium 5 out of 10 on our firmness scale. Press your hand into the Bio-Pur surface and it cradles around your palm, reforming within about two seconds after you lift. Side sleepers benefit most from this: the shoulder sinks roughly an inch into the Bio-Pur while the HIVE layer keeps the hip from dropping too far, which keeps the spine level. Back sleepers under about 230 lbs find the medium firmness delivers enough lumbar support without pushing back uncomfortably. It is a contouring bed, not a bouncy one.

The Casper The One feels firmer than its "medium" marketing label suggests. Independent testers at Tom's Guide, CNET, and Forbes consistently describe it as sitting closer to medium-firm in real use, roughly 6 to 6.5 out of 10. The Breathe Flex top layer is more responsive than memory foam alone, so you get less of the classic sink-in feeling. Back sleepers appreciate that the firmer baseline keeps the lumbar from dropping too far. Stomach sleepers, who typically struggle on softer foam beds because of hip sinkage, often find the Casper's firmer profile more comfortable. For side sleepers, especially those over 150 lbs who need genuine shoulder cradling, the Casper The One can feel too firm at the pressure points.

The firmness difference between these two mattresses is one of the clearest factors in choosing between them. If you sleep on your side, the AS3's medium 5/10 is the correct choice. If you sleep on your back or stomach, the Casper's medium-firm 6/10 has a genuine argument.

Motion Isolation

The AS3 scored 9.4/10 on motion isolation in our vibration-meter testing. The Casper The One scored 8.6/10. Both are all-foam mattresses and both absorb movement more effectively than any hybrid or innerspring at this price. The difference between 9.4 and 8.6 is real but not dramatic. Where it shows up practically is when a partner shifts position at night: the AS3's Bio-Pur layer absorbs the movement almost entirely, while the Casper's more responsive Breathe Flex top layer transmits a small fraction of that motion across the surface.

For most couples, both scores represent excellent isolation. If one partner is a significantly restless sleeper or if one of you is a very light sleeper, the AS3's 9.4 is the safer choice. For solo sleepers or couples who both sleep soundly, the Casper's 8.6 will feel fine.

Cooling Performance

The AS3 scored 8.6/10 on cooling and the Casper The One scored 8.2/10. The AS3's plant-based Bio-Pur foam has a more open cell structure than conventional memory foam, which helps move air through the mattress. The Casper's Breathe Flex top layer is also designed for airflow, and its three-layer build has fewer dense layers to trap heat than older memory foam designs. Neither mattress will leave most sleepers sweating the way traditional viscoelastic foam beds did a decade ago. The cooling gap between these two is narrow. Very hot sleepers will notice the AS3's slight edge. For average sleepers, both beds are adequate.

Edge Support

Edge support on both mattresses is modest, as is typical for all-foam beds without reinforced perimeters. The AS3 scored 7.4/10 and the Casper The One scored 7.2/10, a negligible difference in practice. Sit on the side of either bed to put your shoes on and the foam compresses under you, reducing the effective sleep surface at the very perimeter. Neither mattress is recommended for sleepers who regularly sleep right at the edge or who have mobility concerns that require a stable, firm perimeter for getting in and out of bed. A hybrid with a reinforced coil perimeter would serve that use case better.

Trial Period and Warranty

Both mattresses offer a 100-night sleep trial, so you have the same window to evaluate your purchase with either. Returns are free and handled directly by each brand. Neither requires a reason for the return, only that you have slept on the mattress for a minimum number of nights before initiating a claim.

The warranty gap is where these two diverge clearly. Amerisleep backs the AS3 with a 20-year warranty, covering sagging greater than 1.5 inches and defects in materials or workmanship. Casper backs The One with a 10-year warranty under a similar sagging threshold. If you buy a mattress and sleep on it until it genuinely needs replacing, the AS3's 20-year coverage gives you a longer window of manufacturer protection. The Casper's 10-year warranty is the market standard, not substandard, but the comparison goes to Amerisleep on this dimension.

Price and Value

The Casper The One is the more affordable mattress by a clear margin. Its queen sits between $799 and $999 depending on the active promotion, with MSRP around $999 and 20 percent off sales bringing it to $799. The Amerisleep AS3 queen runs $1,049 to $1,449. At comparable sale pricing, you are typically paying $200 to $300 more for the AS3.

What you get for that premium: better motion isolation (9.4 vs 8.6), a thicker 12-inch profile versus 11 inches, a plant-based foam build, a zoned support layer the Casper does not have, and double the warranty coverage. For couples and side sleepers, the AS3's advantages justify the price difference. For a solo back sleeper on a budget who finds medium-firm foam comfortable, the Casper The One at $799 sale delivers solid value and a Consumer Reports top rating in its segment.

Who Should Buy the Amerisleep AS3

The AS3 is the right choice if you share a bed, sleep on your side, care about foam construction and certifications, or want the longest warranty in this comparison. The HIVE zoned support makes it the more accurate fit for side sleepers over roughly 130 lbs, where shoulder pressure relief and hip support need to work independently. Couples with different sleep styles will find the motion isolation gap between these two mattresses meaningful at 3 AM. The plant-based Bio-Pur foam is also a selling point for anyone who has had off-gassing concerns with conventional polyurethane beds.

Who Should Buy the Casper The One

The Casper The One is the better fit for back sleepers, lighter stomach sleepers, and solo buyers who want a well-regarded all-foam bed from a recognizable brand without paying $1,000 or more. Consumer Reports called it a top all-foam pick in 2025, and independent reviewers from Tom's Guide and Forbes confirm it delivers what Casper promises at the price. If you have slept on medium-firm foam before and liked it, the Casper The One's three-layer build will feel familiar and comfortable. For anyone who finds medium-firmness foam beds too soft under the lower back, the Casper's firmer baseline solves that problem at a lower price than most alternatives in this range.