What Is a Mattress Encasement? (And How It Differs From a Protector)
Related: our protector-vs-encasement guide · our guide to the best encasement for dust-mite allergies.
An encasement is a case for a mattress. It goes over the whole thing — top, sides and base — and closes with a zip. That is the entire definition, and almost every misunderstanding about the product comes from confusing it with something that only covers the top.
How it differs from a sheet, a pad and a protector
A sheet is bedding. It is washed weekly and it protects nothing. A pad adds a layer of comfort and moves around. A protector covers the top surface, usually with a fitted skirt, and lifts off for washing.
An encasement is the only one of the four that encloses the mattress. The distinction is not the fabric or the price; it is whether there is a closure that goes all the way around. No zip, no encasement, regardless of what the packaging says.
What is actually inside one
Three components. A fabric outer layer that you sleep on. A closure — usually a nylon or metal zip with a slider that locks — that runs the full perimeter. And often a thin membrane behind the fabric, which is what stops liquid.
The membrane is the part that gets marketed most and matters least for pest control. A membrane behind an open zip is an open zip. The closure is what makes the product work.
Why they are cut to size
Because the fit is the function. A loose encasement gathers fabric at the seam, and gathered fabric pulls the zip open as the mattress flexes under your weight. That is not a cosmetic problem; it is the exact gap the product was bought to eliminate.
Mattress depth varies from eight to fourteen inches on standard sizes. A cover designed for the middle of that range will not fit either end well. Cutting to the measured depth is why a made-to-order cover costs more than a generic one, and it is also why it works.
Who buys them, and why
Allergy households buy them because dust mites live inside the mattress rather than on the sheets. Rental hosts buy them because the mattress outlives the tenancy. Anyone who has had bed bugs buys one because it stops the mattress being a reservoir. And people with an eight-year-old mattress and sound springs buy one because the surface has worn out and the structure has not.
Those four reasons are most of the market. None of them is about the fabric.
What it costs
A basic encasement runs $80 to $150. A cut-to-size one with a full-perimeter zip runs $200 to $400. The difference is not branding: it is the measurement, the closure quality, and the fact that the cover is made rather than picked from a shelf.
How long it lasts
Five to eight years with spot cleaning and careful zip handling. The zip is the part that fails first, which is why warranty terms tend to focus on it rather than on the fabric, and why fitting instructions spend so much time on keeping fabric out of the teeth.
What it does not do
It does not make a mattress softer, firmer, or newer. It does not kill anything on contact. It does not replace a protector if you want something you can machine wash weekly, because encasements are spot clean only.
What it does is make a mattress clean and enclosed. For an eight-year-old mattress with sound springs, that is most of what "new" used to mean.
What it looks like
A fabric case the size of your mattress, with a zip running around the perimeter and often a flap that covers the slider. It is fitted with the mattress on edge, closed at the corner, and then left alone for years.
What it is not
It is not a sheet, not a mattress pad, not a fitted protector, and not a waterproof sheet. Each of those covers the top only, and each of them comes off for washing.
Why it costs more than a protector
Because it covers five surfaces instead of one, and because it is usually cut to a measured depth rather than picked from a shelf. The measurement is the expensive part, and it is also the part that makes it work.
How it is cleaned
Spot clean only. Vacuum the surface, wipe marks with a barely damp cloth, air it dry. A machine wash distorts the fabric and the fit, and a cover that does not fit is no longer an enclosure.
How long it lasts
Five to eight years. The zip is the part that fails first, which is why the warranty tends to focus on it and why fitting instructions spend so long on keeping fabric out of the teeth.
The simplest definition
If it has no zip around the perimeter, it is not an encasement. That is the whole test, and it works on every product in this category regardless of what the listing claims.
FAQ_FAQ
How do I measure my mattress?
Width, length and depth, with the depth measured at the corner from the sleeping surface to the bottom edge.
Can it be machine washed?
No — spot clean only. A machine wash changes the fit, and the fit is what makes the cover work.
What if the size is wrong?
One free remake within 14 nights of delivery.
Related: Mattress Covers · Comfort Layers · Size Guide · The Ivytress System