If you're shopping for a king size waterproof mattress cover, you've probably noticed the price range goes from $20 to over $100. I bought and tested five covers in my garage workshop—cut, soaked, stretched, and machine-washed them. Here's what actually protects your mattress without feeling like a plastic bag.
Why You Can't Just Buy the Cheapest King Size Waterproof Mattress Cover
I grabbed a $22 Linenspa from Amazon, a $30 SafeRest, a $45 PlushDeluxe, a $70 Coop Home Goods, and a $90 Sleep Number (genuine brand). The cheap Linenspa felt like a shower curtain liner—thin, crinkly, and it slid off the mattress corner on the first night. The Sleep Number was thick but had a weird chemical smell that didn't wash out. The middle-tier covers were quieter and fit better. Price alone doesn't tell you if a king size waterproof mattress cover will breathe or hold up to washing.
How I Tested Each King Size Waterproof Mattress Cover
I ran three tests. First, the moisture barrier: I poured 200ml of water on a stretched section and let it sit for 30 minutes. Second, breathability: I clamped a sample over a steaming cup and measured condensation time. Third, durability: I washed and dried each cover 10 times, then repeated the moisture test. I also measured stretch and fit on my 12-inch thick king mattress. The SafeRest and Coop Home Goods passed the water test every time without leaking—the Linenspa seeped through on wash 7. The PlushDeluxe had good breathability but the seams frayed.
Results: The Best King Size Waterproof Mattress Cover for Most People
The winner is the SafeRest. It's $30, passed all 10 wash cycles, lets air move, and fits my mattress without slipping. The Coop Home Goods came close but costs more than double. If you're on a budget, the SafeRest is the king size waterproof mattress cover I'd buy again. If you want a thinner, softer feel, the Coop is better—but you pay for it.
What About the Premium Options?
The Sleep Number cover is a no-go. It's $90 and smells for weeks. The PlushDeluxe is decent if you find it on sale, but the stitching started to come apart. For most people, spending more than $50 on a king size waterproof mattress cover isn't necessary unless you need specific features like cooling fabric or a terry top. The SafeRest has a cotton terry surface that's comfortable enough.
Final Verdict: Which King Size Waterproof Mattress Cover Should You Buy?
Buy the SafeRest king size waterproof mattress cover. It protects, breathes, and lasts. Skip the cheap Linenspa and the overpriced Sleep Number. I tested it. I own it. You'll save money and sleep better.
Frequently Asked Questions About King Size Waterproof Mattress Covers
Here are answers to common concerns I hear from readers after testing these covers.
**Do king size waterproof mattress covers make noise?**
The sound comes from the material. Vinyl and thin polyethylene covers (like the Linenspa I tested) are loud and crinkly. The middle-tier and premium covers use polyurethane laminate that is silent. In my tests, the SafeRest and Coop Home Goods covers made zero noise. If you're sensitive to sound, choose a cover with a quilted or cotton terry top. Avoid anything labeled "woven" or "vinyl." Also, look for "noiseless" in product titles—but check reviews to confirm.
**Can I use a king size waterproof mattress cover on an adjustable bed?**
Yes, but you need a cover with deep pockets and stretch. Adjustable beds put strain on fitted sheets. I didn't test on an adjustable base, but brands like Coop Home Goods make covers specifically for adjustable frames. Look for pocket depths of at least 14 inches and elastic all around. Avoid covers with elastic only at the corners. The SafeRest also fits well on thick mattresses up to 16 inches, so it should work on adjustable beds. If your bed bends at the foot, make sure the cover is not too tight—it could tear.
**How often should I wash my king size waterproof mattress cover?**
Every 2 to 3 months is a good schedule. If you have allergies, wash monthly. I washed each test cover 10 times to check durability. The SafeRest and Coop Home Goods looked like new after 10 washes. The Linenspa started leaking on wash 7. Use cold water, mild detergent, and dry on low. Never use bleach or fabric softener—they destroy the waterproof layer. Most covers last 2 to 3 years. If you notice peeling or cracking, it's time to replace.
**Does a king size waterproof mattress cover make me sweat?**
It can, but not all do. The waterproof membrane is a barrier to liquids but also to air. Covers with a cotton or bamboo top are more breathable. In my breathability test, the Coop Home Goods cover (bamboo blend) let moisture escape faster than the PlushDeluxe (polyester). If you sleep hot, choose a cover that says "cooling" or "breathable." Avoid 100% polyester outer layers. The SafeRest has a cotton terry surface that is comfortable without adding heat.
**Is a king size waterproof mattress cover safe for kids and pets?**
Absolutely. These covers are great for protecting against spills, bedwetting, and pet accidents. Make sure the cover is non-toxic. The SafeRest is CertiPUR-US certified and has no phthalates or heavy metals. It's machine-washable, which is essential for cleaning after accidents. For pet owners, choose a cover with a stain-resistant outer layer—the terry on the SafeRest can stain if not cleaned quickly. A waterproof cover extends the life of your mattress by keeping moisture out.
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