A bed bug mattress cover, properly called an encasement, works by sealing your mattress in a zippered shell that traps bugs inside and blocks new ones from burrowing in. Any bed bugs already living in the mattress can’t escape or feed through the fabric, and they die of dehydration within roughly 70 days at room temperature. Encasements are one of the most effective tools in a bed bug strategy, but they need specific features to actually work, and they won’t solve an infestation on their own.
How Encasements Actually Work
Bed bugs nest in the seams, folds, and internal cavities of mattresses and box springs because these spots are dark, tight, and close to a sleeping host. An encasement eliminates all of those hiding spots in one step. Once the mattress is fully sealed, trapped bugs have no way to reach you for a blood meal. Without feeding, most bed bugs held at room temperature die within about 70 days. They’re actually dying of dehydration rather than starvation, since the dry environment inside a sealed encasement speeds up fluid loss.
Encasements also make detection far easier. On a bare mattress, bed bugs hide deep in tufts and piping where you can’t see them. On a smooth, light-colored encasement, the dark bugs, their shed skins, and their black fecal spots are much more visible during routine inspections.
Features That Actually Matter
Not every mattress cover qualifies as a bed bug encasement. A standard mattress protector, the kind designed for spills or allergens, typically lacks the construction needed to contain bed bugs. Here’s what separates a functional encasement from a useless one:
- Bite-proof fabric. The material must be dense enough that bed bugs cannot feed through it. If bugs can bite through the cover while you sleep on top of it, the encasement fails its primary purpose.
- Full enclosure. The cover must wrap completely around the mattress with no openings, gaps, or tears. A protector that only covers five sides with an open bottom is not an encasement.
- Bug-proof zipper. The zipper teeth must be very small and close together so that even newly hatched nymphs, which are roughly the size of a poppy seed, cannot weave between them. The zipper must also seal completely at the end-stop with no gap where it terminates.
- Zipper lock or flap. A secondary closure over the zipper pull prevents it from sliding open on its own over time. Some designs use a Velcro flap, others a snap lock.
When shopping, look for products specifically labeled as bed bug encasements rather than mattress protectors. Many manufacturers have their products independently lab-tested to confirm that bed bugs cannot escape or feed through the material. If the packaging doesn’t mention bed bugs at all, it’s likely just a standard protector.
Cover the Box Spring Too
Encasing only the mattress leaves a major hiding spot exposed. Box springs are actually a preferred harborage for bed bugs because the open internal frame, stapled fabric, and wooden slats create dozens of crevices. Sealing both the mattress and box spring eliminates the two largest reservoirs of bugs in a bedroom. If you have a platform bed with no box spring, you only need the mattress encasement, but inspect the platform’s joints and slats regularly.
How Long to Leave the Encasement On
The encasement needs to stay on continuously, not just for a few weeks. While most trapped bugs die within 70 days, that timeline assumes consistent room temperature. Cooler conditions can extend survival. Older studies from the 1930s and 1940s suggested bed bugs could survive over a year without feeding, but those experiments involved unheated European homes where temperatures dropped below 40°F. Modern research on bed bugs collected from climate-controlled U.S. homes puts the realistic limit at about 70 days on average.
To be safe, plan to keep the encasement on for at least a full year, ideally as a permanent fixture. Many encasements are designed to be comfortable enough for long-term use, and they also protect against dust mites and spills. Inspect the surface periodically for tears, especially around the zipper. If the encasement rips or the zipper fails, any surviving bugs inside can escape, and you’re back to square one.
Washing and Maintenance
You don’t need to remove the encasement to wash it. Your regular fitted sheet goes over it as usual, and you wash your sheets and pillowcases on your normal schedule. If you do need to launder the encasement itself, check the manufacturer’s instructions, but most can handle a standard machine cycle. For any bedding that may have been exposed to bed bugs, running it through a dryer set on high for 30 minutes kills all life stages, including eggs. The heat, not the washing, is what does the work.
What Encasements Won’t Do
An encasement handles the bugs living inside your mattress and box spring. It does nothing about the ones hiding in your bed frame, nightstand, baseboards, electrical outlets, carpet edges, or behind picture frames. Bed bugs are flat enough to slip into any crack that fits a credit card, and a bedroom infestation typically involves multiple hiding spots beyond the mattress.
Think of encasements as one layer of a broader approach. They remove the mattress as a hiding spot, protect your investment in the mattress itself (so you don’t have to throw it away), and make ongoing monitoring simpler. But they work best alongside thorough vacuuming, targeted treatment of other harborage areas, and interceptor traps placed under the bed legs to catch bugs traveling to and from the bed. For moderate to heavy infestations, professional treatment is typically needed to reach bugs in walls and furniture that no encasement can touch.
Choosing the Right Size
Encasements need to fit snugly. A cover that’s too large will bunch up and create folds where bugs can hide on the outer surface, defeating part of the purpose. A cover that’s too small won’t zip shut or will strain the fabric and zipper under tension, increasing the risk of failure. Measure your mattress depth (thickness) before ordering, not just the standard size like queen or king. Pillow-top and hybrid mattresses often run 14 to 16 inches deep, and a standard-depth encasement won’t close over them. Most manufacturers list a depth range on the packaging.
For box springs, measure separately. Box springs are usually thinner than the mattress, and using a mattress-sized encasement on a box spring leaves excess fabric that bunches and creates new hiding spots. Many brands sell box spring encasements as a separate product with the correct dimensions.