Side, back or stomach: which pillow for which position?
You may already have changed pillows two or three times without anything improving. That is normal: most people choose a pillow by its material — foam, feather, latex — when that is not the deciding factor.
A study published in Applied Ergonomics compared the influence of material, firmness, shape and height on cervical alignment during the night. One factor came out clearly ahead of the others: height. In other words, a memory foam pillow at the wrong height will do you more harm than a basic pillow at the right one.
And the height that suits you depends almost entirely on one thing: the position you sleep in.
This article deals specifically with the relationship between position and height. For the full set of criteria — foam density, lifespan, contoured shapes, when to replace — see our complete guide to choosing a pillow.
The ten-second test
Before we talk numbers, lie down in your usual position and ask someone to look at you from the front, or take a photo of yourself.
Your ear should line up with your shoulder, and your spine should form a continuous line, with no break at the neck. If your head tips upwards, your pillow is too thick. If it leans towards the mattress, it is too flat.
This detail is not cosmetic. When the height is wrong, the neck muscles work to hold the head up — for seven or eight hours straight. That prolonged contraction is what you feel on waking as stiffness, and sometimes as tension running down into the shoulders or upper back.
You sleep on your side
It is the most common position, and the one that needs the most height: between 10 and 15 cm.
The reason is purely geometric. On your side, your shoulder creates a gap between your ear and the mattress, and the width of that gap matches the width of your shoulders. The pillow has to fill it completely, otherwise your head drops all night.
It is also why broad-shouldered side sleepers need a distinctly thicker pillow than average — and why a "universal" pillow almost always disappoints them.
Two further points if this is you. Your ear is compressed for hours, which makes conventional ear plugs painful fairly quickly. And your cheek stays pressed against the fabric, which explains the morning creases we cover in this article.
Finally, on your side the body has a second unsupported point that almost nobody addresses: the space between your knees. That is the subject of our guide for side sleepers.
You sleep on your back
You need less height: between 8 and 12 cm.
On your back, there is no shoulder to compensate for. The goal changes: it is about supporting the natural curve of the neck without pushing the head forward. A pillow that is too thick puts your chin towards your chest, which stretches the muscles at the back of the neck all night and can also restrict breathing.
This is where contoured pillows make full sense: the higher ridge sits under the neck, while the hollower centre cradles the back of the skull.
You sleep on your stomach
Let us be direct: it is the hardest position to reconcile with a relaxed neck. Sleeping face down forces you to turn your head 25 to 35 degrees simply to breathe, and to hold that rotation all night.
If this is your position, the rule inverts: you need very little height, under 7 cm — or no pillow at all under your head. Many physiotherapists suggest sliding a thin one under the hips instead, to stop the lower back from arching.
We will not tell you to change position: you do not really choose how you sleep, and forcing it mostly produces restless nights. That said, if you regularly wake with a locked neck and you sleep on your stomach, trying a transition to your side over a few weeks is the most useful avenue — the available work shows a clear improvement in neck pain among those who manage it.
What memory foam changes
A conventional pillow compresses under the weight of the head: its height at bedtime is not the height it will have at three in the morning. That is why so many people feel their pillow "doesn't hold".
Memory foam of good density keeps its height all night and spreads pressure instead of concentrating it on one point. That is what allows a correctly chosen height to stay correct until morning.
Its known flaw is heat: dense foam naturally retains body temperature. That is why we pair it with wide 3D mesh side panels and a breathable cover — the subject of our article on waking up drenched.
In short
On your side, aim for 10 to 15 cm. On your back, 8 to 12 cm. On your stomach, under 7 cm or nothing. And in every case, check the ear-shoulder alignment: it is the only test that really counts, and it costs nothing.
If you wake with a stiff neck despite a recent pillow, the material is probably not the problem. It is the height.
To go further on the other criteria — density, longevity, shape — our complete guide to choosing a pillow covers the lot.
Discover the Restelya Cervical Pillow →
This article is informational and does not replace the advice of a healthcare professional. If your neck pain is intense, persistent or accompanied by tingling, consult a doctor or a physiotherapist.