All four that I bought (2 sets of 2) seems to be working just fine. This is the first set that we didn't buy that didn't zip around the entire mattress.
Twin Size Zippered Mattress Protector Encasement - Premium Terry Absorbent Cover With Six-Sided Waterproof Protection - Quiet, Breathable, And Fully Washable
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Protect Your Twin Mattress With Zippered Waterproof Encasements - Twin 2 Pack Included
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Biloban Box Spring Cover (4/5/7/9/13/17Inches) Twin, High Profile Waterproof Mattress Protector, 6 Sides Wrapping Zippered Mattress Encasement Cover
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Twin Mattress Protector Waterproof Soft & Breathable Terry, Noiseless Mattress Cover Fits Up -14'' Depth, Skin-Friendly Machine Wash Mattress Protector
29 Review
Heavy Duty Waterproof Aozzy Air Conditioner Cover For Outdoor Window Units With Adjustable Straps - 17" W X 12" D X 13" H Inches
31 Review
Gulrear Portable AC Window Seal Kit - White 400CM/158Inch Hot Air Stop Exchange Guards With Zipper And Adhesive Fastener
38 Review
Black 2-Pack Of Vivere EFHTS Accessories For Hammocks
27 Review
LOFTEK LED Dimmable Floating Pool Lights Ball, 16-Inch Cordless Night Light With Remote, 16 RGB Colors & 4 Modes, Rechargeable & Waterproof, Perfect For Indoor/Outdoor, Exhibition Decor, 1-Pack
38 Review