An air mattress should be firm enough to keep your spine aligned but soft enough that your shoulders and hips can sink in slightly. For most people, that means inflating to about 90% capacity, then fine-tuning from there. A fully inflated air mattress is almost always too firm, and the “perfect” level depends on your body weight, sleep position, and whether the mattress is brand new.
Why Medium-Firm Beats Fully Inflated
A systematic review published in the Journal of Orthopaedics and Traumatology found that a medium-firm surface promotes the best combination of comfort, sleep quality, and spinal alignment. The goal is for your spine to maintain the same natural curve it has when you’re standing upright. A mattress that’s too firm prevents your shoulders from sinking in at all, which forces your neck and upper back out of alignment and leads to joint stiffness. One that’s too soft lets your hips and shoulders drop too far, creating a hammock effect that strains your lower back.
With an air mattress, you have a built-in advantage: you can adjust firmness in real time. The same review noted that a customized inflation mattress provided better spinal support during side sleeping than any single fixed-firmness option. That’s essentially what you’re doing every time you add or release air.
How to Find the Right Level
Start by inflating the mattress fully using its pump, then lie down in your usual sleep position. You’re checking two things: whether your hips touch the floor or base beneath the mattress (too soft), and whether you feel like you’re perched on top rather than cradled by the surface (too firm). Most people need to release a small amount of air from a fully inflated mattress to reach a comfortable middle ground.
A simple test: slide your hand under the small of your back while lying face up. If there’s a large gap, the mattress is too firm and your lower back isn’t being supported. If your hips feel like they’re sinking below your chest, it’s too soft. When your spine feels relatively neutral, with gentle support under your lower back and your shoulders resting comfortably, you’re in the right range.
Adjusting for Sleep Position
Your sleep position changes which parts of your body bear the most pressure, so it also changes how much air you need.
- Side sleepers need a slightly softer surface so the shoulder and hip on the downside can sink in. If the mattress is too firm, those pressure points get compressed, which can restrict blood flow and cause numbness or tingling. Side sleepers under 130 pounds generally do best on a soft to medium surface, those between 130 and 230 pounds on medium to medium-firm, and those over 230 pounds on a firmer setting that prevents bottoming out.
- Back sleepers need moderate firmness to support the lumbar curve without creating a gap under the lower back. A medium-firm level works for most back sleepers up to 230 pounds.
- Stomach sleepers need the firmest setting of the three positions. A softer surface lets the pelvis sink, which hyperextends the lower back. If you sleep on your stomach, keep the mattress closer to full inflation and only release a small amount of air.
Body Weight Changes Everything
A 120-pound person and a 220-pound person on the same air mattress at the same inflation level will have completely different experiences. Heavier bodies compress the air inside more, so what feels firm to a lighter person may feel like bottoming out for someone heavier. If you weigh over 200 pounds, you’ll likely need the mattress closer to full inflation, and you may want to check that the mattress’s weight capacity gives you enough headroom. If you’re under 150 pounds, you can afford to let more air out for a softer, more contouring feel without risking contact with the ground.
When two people of different weights share an air mattress, compromise is inevitable. The heavier person’s side will compress more, and there’s no zone-by-zone adjustment like you’d find on a dual-chamber mattress. Inflating to a level that keeps the heavier sleeper supported is the safer default, since sleeping too soft causes more alignment problems than sleeping slightly too firm.
New Air Mattresses Lose Firmness Overnight
If your air mattress feels noticeably softer the morning after you first inflate it, that’s normal. The PVC or vinyl material stretches when it’s inflated for the first time, which reduces internal pressure even without a leak. Coleman’s support documentation confirms this is expected behavior and not a sign of a puncture. You may need to top off the air for the first few nights until the material finishes stretching and stabilizes. After that initial break-in period, a well-sealed mattress should hold its firmness through the night with minimal loss.
If the mattress continues losing significant air after the first week, that’s a different issue and likely indicates an actual leak, often at a seam or around the valve.
Risks of Over-Inflating
Pumping an air mattress to maximum capacity and then some doesn’t just make it uncomfortable. Over-inflation puts excessive stress on seams and material, which can lead to rupture. The most common failure points are the seams along the edges and the internal baffles that create the mattress’s shape. A mattress inflated past its recommended pressure can also develop a visible bulge on one side, which is a warning sign that a blowout is coming.
Beyond durability, a rock-hard air mattress creates concentrated pressure on your hips, heels, and shoulder blades. Sustained pressure on these bony areas compresses blood vessels and nerves, which is why you wake up sore or with a numb arm. Releasing even a small amount of air distributes your weight across a larger surface area and reduces those pressure peaks considerably.
A Quick Nightly Check
Air mattresses respond to temperature. Cool night air causes the air inside to contract slightly, making the mattress feel softer by morning. If you’re setting up in a tent or unheated room, inflate the mattress after the ambient temperature has dropped rather than during the warmth of the afternoon. This way you won’t wake up on a half-deflated surface at 3 a.m. A few extra pumps of air right before bed, just enough to restore that medium-firm feel, can make the difference between a decent night’s sleep and a miserable one.