Five sides or six: which cover your problem actually needs

Two covers sit side by side on the same shelf. One slips over the mattress like a fitted sheet. The other swallows it and zips shut. They cost about the same, they carry the same word on the label, and they answer different questions.

General information about published federal guidance, read at the source on the date shown beside the link. It is not medical or pest control advice.

Two shapes, and the gap between them

A fitted protector has five sides: a top panel and four short walls, with elastic gathering the whole thing underneath. Put it on and the mattress top is covered, the sides are covered to a few inches down, and the bottom face of the mattress is open to the room.

An encasement has six. The mattress goes inside it the way a duvet goes inside a cover, and a zip runs round three edges to close the last gap. Nothing crosses the fabric after that.

That sixth side is the whole difference. It changes nothing about spills, since a drink lands on the top face either way. It changes everything about anything alive, because an insect that can walk round the edge of a five-sided cover cannot walk through a closed one.

What sealed means, in the government's own words

The Environmental Protection Agency publishes a page on treating bed bugs without calling anyone. It lists the non-chemical steps first, and one of them is a cover.

“Purchase protective covers that seal mattresses and box springs. With covers that seal, the bed bugs will get trapped inside and die”

Read the wording closely, because it does the work. The word is seal, twice. Not cover, not protect. The mechanism described is a trap: the insects that were already inside the mattress stay inside, cannot reach a host, and die there.

A five-sided protector cannot do that, and nothing about the fabric is the reason. The reason is arithmetic. Leave one face open and you have left a door.

The same page warns that heat treatments done at home may not work on their own, which is worth holding onto if you are planning to deal with this without help. A cover is one step among several, not a cure.

Our range, counted by shape

We make both. Of the 50 covers on this site, 29 are fitted and five-sided, and 21 zip closed on six. Neither number is a headline: they are close because the two problems are both common.

The departments split cleanly. Fitted protectors and the quilted CloudGuard pads are five-sided. Mattress encasements, box spring encasements and pillow covers all zip.

If the problem is liquid

Buy the fitted protector. A spill lands on the top face, the waterproof backing stops it there, and you strip the bed and put the cover in the machine the same way you do the sheets.

An encasement handles the same spill, and then makes you unzip a mattress at eleven at night while somebody stands in the hall in wet pyjamas. For a house with young children, a fitted protector on the bed and a spare in the cupboard beats anything clever.

• Toilet training, a sick child, a dog with opinions about the bed: fitted protector.
• A mattress still under a manufacturer warranty that a stain would void: fitted protector, and keep the receipt.
• Someone who will not put the cover back on if it takes more than a minute: fitted protector.

If the problem is bed bugs

Buy the encasement, and buy one for the base at the same time. The federal wording above names mattresses and box springs together, and it does that because a hollow wooden frame with fabric stapled over it is better shelter than a solid mattress.

Then leave it alone. A cover bought for this reason works by time: whatever was sealed in has no way to feed. Unzipping it in three weeks to check undoes the point of it.

Check the zip end when you fit it. That is the one spot where a gap can survive, and it is worth two minutes of your attention while the mattress is still on its side.

If the problem is allergy

Dust mites live in the mattress and the pillow, and what triggers asthma is not the mite but what it leaves behind. A closed cover keeps that material on the far side of the fabric from your face.

Cover the pillows as well. The pillow is the item that touches a face for eight hours, and it is the one people skip. Our guide on dust mites covers the washing half of the job, which matters as much as the cover does.

If the mattress has gone hard

Neither shape fixes that on its own, so we make a third thing. The quilted protectors add loft between you and the mattress while still carrying a waterproof back. They are five-sided, they wash like a protector, and they sleep warmer than a thin one.

If you run hot, this is the wrong department and the thin fitted protectors are the right one. There is no version of a quilted pad that does not hold some heat.

The half of the bed people forget

A mattress sits on something. If that something is a box spring or a fabric-covered foundation, it has a hollow inside and it is part of the same problem.

Box spring encasements are cut shallow, because a base is shallower than a mattress, and the ones here run from up to 9 in to up to 9 in. Measure yours before ordering. A foundation and a box spring sold as the same size can differ by four inches of height.

The cover goes on once and lives out of sight underneath the bed. Nobody looks at it again, which is the point.

Living with each one

The fitted protector is the one you will actually maintain. It comes off in a second, goes back on in ten, and survives a warm wash and a cool tumble as often as you need it to.

The encasement is a project once and then invisible. Fitting one means stripping the bed, lifting the mattress on its side and walking the cover up it, which is a two-person job on a king. After that it stays put for months.

Both make some noise if you go looking for it. The face fabric is what decides that, not the shape: a terry or knit face muffles the membrane, and a bare film face does not. Of the covers here, 6 carry a cotton terry face.

What neither cover does

Neither one stops a spill that runs off the side and into the mattress seam before you get there. Waterproof describes the panel, not the geometry of a mug of tea.

Neither one makes an old mattress supportive again. A pad adds loft on top and cannot put a spine back in the middle of a bed that has collapsed.

And neither one is a treatment. A sealed encasement is one of several steps against bed bugs, in the same list as the dryer and the vacuum, and the federal page says as much on its own front page.

What both do is buy time on the most expensive thing in the bedroom. Put the cover on before the reason arrives, because everything on this page works better in advance than in response.