Pickup truck bed covers -- how waterproof are they?

I’m not referring to a cap, but a flat cover. One that covers the whole bed, not the foot locker kind of things that sit near the front of the bed.

I presume there are many varieties – I’m wondering how waterproof the most waterproof ones are. TIA.

I have an Extang tonneau cover.

It has a channel lock instead of buttons. Never had anything penetrate it.

I live in the NorthEast U.S.A. It has seen –5 degrees with blizzard conditions…ice…sleet…heavy snow pile up… and 110 degrees w/ heavy tropical storm winds and rain, along with a Nor’ Easter here and there… Not a drop got through.

One small problem is that very cold weather shrinks the material and makes it darn tough to secure it.

I have one of the fiberglass ones with the struts to hold it open(hinges toward the cab. Did pretty well until the weatherstip came unglued(after 8 years or so)

I second what Philster said. I also had an Extang with the channel lock* that never let in a drop, despite all sorts of awful conditions. I’d highly recommend the brand. The upside to a soft tonneau is that it can be rolled up to allow oversize cargo. A hard shell cover can be opened as well, but is much more expensive and is limited to cargo no larger than the triangle formed between the bed and the raised shell. The downside to a soft cover – well, see below.

While the cover kept out moisture, it was not – alas – impervious to the knife that some fuckwad decided to stick in it and run down the length of the tonneau. So, depending on where you live (and the incidence of random vandalism), you might want to consider something a little more sturdy.
*(The channel lock is one curved rigid strip running the length of the cover that locks into a corresponding curve on the tonneau frame – kind of like this ¿? . It works quite nicely at keeping out water as there’s a continuous seal rather than only at each button. Also, it looks a bit sleeker since you don’t have a metal stud sticking out every eight inches.)

My FIL has one like Philster described. So far, its survived 7 winters and summers, with temps as high as 38 celcius and as low as -42C. It almost as good as new and not leaked once. Get a good brand name and you should be very happy.

I would strongly caution against the button-down style. I have seen those rip.