This listing is bed protection you lay on a mattress. Reusable Bed Pad (XXL 36 by 76 Inch) is listed as a waterproof, washable, nonslip incontinence underpad with tuck-ins, for king and California king beds, at $39.99 when this article was written. The notes say those tuck-in sides let it stand in for a mattress protector. The title also names adults and pets. The listing details are the ones current when the article was written. Check the Amazon page before you buy. We are not reviewing washable incontinence panties, because we do not have a verified product for that. This is not medical advice, and we did not launder a sample as a lab test.
Thirty-six by seventy-six inches is a long runner. Across a king or a California king, 36 inches covers a wide center panel. It does not reach both side edges of a king mattress on its own. Down the length, 76 inches covers most of an adult sleeper from pillow to feet on many beds, and it may come up short on a very tall person or a bed with a deep pillow stack. Look at your mattress before you call it full coverage.

Tuck-ins, waterproof backing, and a single pad
The listing’s tuck-ins are flaps you push under the mattress so the pad does not skate off the middle of the bed. Use them. A waterproof pad that bunches at the hips protects a smaller square than the one you paid for. Nonslip is the other stay-put claim. It should face the way the product indicates. Read the label on the pad you receive. Our notes do not include a photo of which side is which.
Waterproof, on an underpad, means the listing says fluid should not pass through to the mattress. The top still absorbs or holds. If someone floods past the edges, the mattress is exposed around the pad. A fitted sheet over the pad can keep it comfortable and still let you know when the surface is wet. A pile of blankets on top will not stop a leak at 3 a.m.

You are buying one pad at $39.99. One pad only works if you have a plan for wash day. Many homes keep two of something this size so one is on the bed while the other is in the machine. We can only price the single listing we checked. A second one is a second purchase at whatever the page shows then.
The listing is here: the washable XXL underpad on Amazon.
Washing a pad that lives on the bed
Follow the care label sewn into the pad you get. We are not going to invent a dryer temperature or a bleach rule the listing notes did not give us. Shake off debris, wash it the way the label says, and dry it fully before it goes back on the bed. A damp waterproof pad trapped under a sheet is a smell problem waiting a day. Skip fabric softener if the label tells you to, and if the label is silent, softener is still a good thing to avoid on absorbent cloth because it can coat the fibers.
The title includes pets. That is a listing fact. If a dog shares the bed, the same pad is being asked to handle a different kind of mess, and you may want it on top of the sheet where you can grab it. For an adult sleeper, under the hips is the usual zone. Do not cut the tuck-ins off to make it “fit” a twin. This size is described for king and California king.
It is still an underpad. It will not walk to the bathroom with you. Daytime protection, if you need it, is a pad, a guard, or a pull-up from its own listing. Mixing those jobs onto a bed pad is how people get disappointed in a perfectly ordinary piece of cloth.
A comparison of bed-pad sizes is on the site at the bed-pad size comparison. Other sizes are discussed there, not here. This page is the washable 36 by 76 underpad only. Check the Amazon listing before you buy. Dimensions, tuck-ins, waterproof wording, and the price were current when the article was written.