Mattress Toppers NZ: 5cm or 8cm, and When a Topper Won't Help

Most topper guides open by asking how thick you want it. That is the wrong first question. The useful first question is what is actually wrong with your bed, because three different problems get sold the same product, and only one of them is a problem a topper can solve.

Everything below is measured from the toppers we import and stock, so the specifications are from our own records rather than generic advice. Where we cite outside research we say what it did and did not test. Last updated 12 August 2026; specifications and stock are checked against our own records on the date shown.

We stock three foam toppers in all six New Zealand bed sizes. They come from one supplier, share the same bamboo-fabric cover and the same non-slip base, and differ only in what is inside. That makes them unusually easy to compare against each other — which is what this guide does. It also means we can tell you, with our own products as the evidence, that two things the market treats as decisive are not.

What does a mattress topper actually fix?

A topper changes the surface you lie on. It does not change the support underneath it. That single sentence decides most purchases.

Beds go wrong in three different ways, and they are not interchangeable:

If you are in the second or third row, a topper is the wrong purchase and no thickness changes that. We would rather say so here than have you find out after it arrives.

Will a topper fix a sagging mattress?

No — and there is a two-minute test that settles it before you spend anything.

Strip the bed. Lay something rigid and straight across the mattress from side to side — a broom handle, a spirit level, the edge of a bookshelf. Look at the gap underneath at the worst point.

• No visible gap — no obvious sagging, so the surface is the likely problem. A topper will change how it feels.
• A visible dip — the support layer has gone. A topper will settle into the dip and you will have paid to move the problem up eight centimetres.

The same applies if you can feel individual springs, or if one side has clearly compressed more than the other. Those are structural failures. Foam laid on top conforms to the shape underneath it; that is what foam does.

How thick should a mattress topper be — 5cm or 8cm?

Thickness is not a quality ladder. It is a matching problem. Published guidance in this category disagrees with itself: some NZ and Australian guides call 7–8cm the sweet spot, while others warn that 8cm and over can overwhelm the mattress under it and lift the bed higher than your sheets can cope with. Both are right, for different beds.

Here is how we would put it, given we sell both:

Add the topper depth to your mattress depth before you order. That total is what your fitted sheet has to cover. An 8cm topper on a 30cm mattress needs a sheet that will stretch over 38cm, and a lot of standard sheets stop short of that. It is the kind of thing that gets discovered on the night the topper arrives, and it is entirely avoidable with a tape measure.

Does foam density tell you how firm a topper feels?

No. Density and firmness are different measurements, and almost every listing in this category blurs them.

Density, quoted in kg/m³, is how much foam is packed into a given volume. It predicts durability — how long before the topper develops a permanent body impression. Firmness is a separate measurement (ILD, or indentation load deflection) describing how much force it takes to compress the foam. A high-density foam can be soft. A low-density foam can be firm.

We can prove that with our own product rather than asking you to take it on faith. Our Dream Flip Dual Sided topper is 8cm built as two bonded 4cm layers — and the firmer face is the lower-density foam of the two. The soft face is gel memory foam at 40kg/m³; the firm face is a lower-density support foam. If density set firmness, that topper would work the other way around.

So when you see a density figure on a topper listing — including ours — read it as "how long will this last", not "how soft is this".

One thing we will not do is quote you a firmness rating. Our manufacturer does not publish an ILD figure for these foams, so we do not have a tested number to give you. We describe feel from the construction and from handling the product. Anyone who hands you a precise firmness number should be able to tell you how it was measured.

Which topper matches which problem?

All three share the same cover, the same three-sided zip and the same non-slip base. The differences are entirely in the foam.

The weights in that table are worth a second look, because they are the one specification here that cannot be argued with. The Comfort Plush Queen is 11.3kg and the Dream Flip Queen is 10kg — same 8cm, same nominal density on the memory foam. The difference is that the Dream Flip spends half its thickness on a support layer, and the Comfort Plush is memory foam all the way down. That is the whole distinction between them, expressed in a number you can check on the scales.

If two of you disagree about firmness, that is more common than the category admits, and it is not a matter of one person being fussy. The same surface genuinely feels different to different people: a heavier sleeper compresses foam further and finds it softer, a lighter sleeper barely compresses it and finds the same product firm. Sleeping position pulls in another direction again — side sleeping drives your weight through two narrow points, the shoulder and the hip, while sleeping on your back spreads it along the whole length of you.

You cannot resolve that by reading specifications, and if you are buying online you cannot resolve it by lying on the thing either. That is the case the Dream Flip Dual Sided exists for: two faces, turn it over, keep the side that suits the bed.

Is a firmer or softer surface better for back pain?

The best evidence in this area points toward medium-firm rather than firm, and it is worth knowing exactly what it says and does not say.

A randomised, double-blind trial of 313 adults with chronic non-specific lower back pain (Kovacs et al., The Lancet, 2003) compared a medium-firm mattress against a firm one over 90 days. The medium-firm group had roughly double the adjusted odds of improvement in pain while lying in bed (odds ratio 2.36) and in pain-related disability (2.10). Those are the adjusted figures; the unadjusted comparison did not reach significance, which is worth knowing if you are weighing how strong this evidence is. A 2015 systematic review of 24 controlled trials (Radwan et al., Sleep Health) reached a compatible conclusion, and added something we did not expect to be able to use: its optimum was a surface that is medium-firm and self-adjusted by the sleeper. Most toppers cannot be adjusted at all. A two-sided one can be turned over, which is the cheapest version of that idea we know of.

Neither study tested a topper, and both looked at people who already had chronic back pain. We are not claiming a topper treats anything. What that research tells you is the direction to move a bed that is too hard, and a topper is the inexpensive way to move it. Hotels are built the same way — a supportive mattress with a softer layer over it — though that is an observation about how beds are assembled, not a finding from the studies above.

What size do I need?

Our toppers are cut to New Zealand bed sizes, which are not the same as US or UK sizes. Measure your mattress rather than trusting the label on a bed you inherited.

Two size notes worth acting on. If the sleeper is a child who is still growing, a King Single is 17cm wider and 13cm longer than a Single, and buying the bed they will need in two years is cheaper than buying twice. If you are over about 180cm tall, check the length column: Double is 188cm, which is 15cm shorter than Queen.

Does gel actually keep you cooler?

Less than the marketing implies. Gel infusion gives foam something to absorb heat into, so it starts out cooler than plain memory foam — but a gel bead has no way to shed that heat once it has taken it, so the advantage narrows as the night goes on. We have not measured how long it lasts on these toppers, so we are not going to give you a number for it.

All three of our toppers use gel-infused foam, and we would rather set the expectation properly than sell you on it. If sleeping hot is the main reason you are shopping, airflow under you and a breathable cover will do more than the gel does — and a wool topper would do more than any foam one. We do not sell a wool topper. If that is what your problem calls for, buy one from someone who does.

How do you look after a foam topper?

The cover on all three unzips on three sides and comes off completely, which matters more than it sounds.

• Wash the cover, not the foam. Memory foam should never go in a washing machine — it tears when saturated and takes days to dry through. Check the care label on your cover for the temperature.
• Check your machine will actually take it. The cover itself only weighs about a kilogram, so weight is never the limit — drum space is. Fabric that is packed in tight does not tumble, and fabric that does not tumble does not rinse. Sizes below.
• On dust mites: washing removes the large majority of dust-mite allergen even on a cool cycle, which is most of what a person with allergies is reacting to. To kill the mites themselves, ASCIA — the allergy specialists' body for Australia and New Zealand — recommends washing bedding at over 60°C. A heated front-loader will reach that; a cold-fill top-loader will not, and if that is what you have, ASCIA's alternative is a eucalyptus or tea-tree laundry product in a cold wash, or ten minutes in a hot dryer afterwards. Either way, a cover you can take off and wash beats a topper you cannot, which is most of them.
• Rotate it head to foot every few months so the same spot is not always taking your hips.
• Air it before you use it. Foam that has been compressed for shipping needs time to come back to full thickness, and new foam has a smell when it comes out of the bag. We have not timed either on these toppers, so we will not pretend to a number — unzip the cover, leave it off, give it a well-ventilated room, and put it on the bed when it looks and smells right.
• If it slides, the usual cause is a slick mattress protector underneath. A non-slip base grips fabric, not plastic. Put the topper directly on the mattress and the fitted sheet over the top of both.

What size washing machine does the cover need?

Work it out from fabric area, not weight. A topper cover is a top panel, a bottom panel and a band of side fabric, so the area is roughly twice the bed size plus the sides — and that is what has to tumble freely in the drum.

Those are computed from the cover's own dimensions, not from a load test — if your machine already handles a double duvet cover comfortably, it will handle any of these. Wash the cover on its own. Putting it in with a load of towels is what turns an adequate drum into a packed one.

How long does the cover take to dry?

Longer than a sheet of the same size, and for a reason worth knowing: the underside does not breathe. The face and sides are bamboo-blend fabric, but the base is a non-slip coated fabric — that coating is what stops the topper sliding, and it also means moisture can only leave through one face.

So the thing that decides your drying time is not the weather, it is how you hang it:

• Hung open — across two lines, over a clothes horse, or pegged flat so air reaches both faces: a warm breezy day will usually do it in around four to six hours.
• Folded over a single line — the coated side ends up against itself and traps the moisture. Expect it to take roughly twice as long, and to still feel cool and damp along the fold.
• Cool or still day — plan on overnight, and bring it in and finish it indoors rather than leaving it out to collect dew.

These are estimates from the material and the construction, not stopwatch measurements, so treat them as planning numbers. The safe rule: wash it on a morning when you do not need the bed made by evening. Bamboo viscose also holds more water than cotton does, which is the other half of why it is slower than the sheet you washed with it.

Do not tumble dry it on heat. The non-slip coating is the part that fails first, and once it has gone the topper starts travelling in the night.

Frequently asked questions

Will a mattress topper fix a sagging mattress?

No. Lay a straight edge across the mattress and look at the gap underneath. If there is a visible dip, the support layer has failed and foam laid over it will settle into the same shape. You need a mattress, not a topper.

Is 5cm or 8cm better for a mattress topper?

Neither is better in general. Choose 5cm when the bed is only slightly firmer than you want and you do not want to raise it much. Choose 8cm when the mattress supports you properly but the surface is genuinely hard. Add the topper depth to your mattress depth and check your fitted sheet will cover the total before ordering.

Does a higher density foam mean a firmer topper?

No. Density is how much foam is in a given volume and predicts durability, not feel. Firmness is a separate measurement. On our own Dream Flip Dual Sided topper, the firmer of the two faces is the lower-density foam.

Will my fitted sheet still fit with a topper on?

Only if its pocket depth covers your mattress depth plus the topper. An 8cm topper on a 30cm mattress needs a sheet that stretches over 38cm. Measure before you order — this is the most common complaint about thick toppers and it is avoidable.

What is the difference between the Dream Flip and the Comfort Plush?

Both are 8cm. The Comfort Plush is gel memory foam the whole way through and is the softer, heavier of the two — 11.3kg in Queen. The Dream Flip is two bonded 4cm layers, gel memory foam on one face and a firmer support foam on the other, so you can turn it over and change the feel. It weighs 10kg in Queen.

What does five-zone mean on a mattress topper?

On our 5 Zone topper the foam surface is pressed into five profiled sections, so it does not compress identically across the whole area. The zoning is formed in the foam itself, not printed on the cover.

Can I put a mattress topper on a new mattress?

Yes, and it is a common fix when a new mattress turns out firmer than it felt in a showroom. Warranty terms differ by manufacturer, so check yours before you add anything on top. If the new mattress is too soft rather than too hard, a topper will make that worse.

Can you wash a memory foam mattress topper?

Wash the cover, never the foam. All three of ours have covers that unzip on three sides and come off completely. Saturated memory foam tears easily and can take days to dry through.

Which topper is best for side sleepers?

Side sleeping concentrates your weight at the shoulder and hip, so a deeper, softer surface usually suits it better — the 8cm Comfort Plush, or the soft face of the Dream Flip. If you share the bed with a back sleeper, the Dream Flip lets you settle the argument after it arrives rather than before.

How long does a mattress topper last?

That depends more on density than on thickness, which is what the density figure is actually useful for. Body impressions that do not recover overnight are the sign it is finished. Rotating it head to foot every few months spreads the load.

Where to start

If you take one thing from this: do the straight-edge test first. It costs two minutes and it is the difference between a topper that fixes your bed and a topper that inherits its problems.

If the mattress is sound and only the surface is wrong, the choice is narrow. Slightly firm, and you want minimal added height: the 5 Zone Gel Memory Foam Topper. Genuinely hard, and you want the surface properly changed: the Comfort Plush Gel Topper. Not sure, or two of you disagree: the Dream Flip Dual Sided, and decide over a few nights instead of at checkout.

All three come in every New Zealand bed size from Single to Super King. We have not quoted prices here because they change; the current price is on each product page.

Written by Eric, founder of HomeMart, with 20 years in furniture procurement. If something here is wrong, or a topper did not behave the way this guide says it would, tell us and we will correct the page.

Related reading: Mattress Buying Guide: How to Choose the Right Mattress in NZ — start there if the straight-edge test told you the mattress itself has gone.