Tile coach has some pretty great videos where he tests the waterproofness of foam board vs membrane and membrane wins (albeit, marginally). The membrane waterproofing is thicker than the felt that comes preinstalled on the kerdi board. With all the requisite seam/corner/screw taping, I feel great peace of mind using membrane over concrete board, and it’s cheaper. However, for the ease of installation and ability to wet shim, kerdi board is a great option, it’s just very $$. For professionals who are trying to move quickly and save time, I think foam board is a great option. However for a DIY bathroom, you’re going to be going slow anyways, so why not save your money and get the best shot at waterproofing correctly (I emphasize correctly because there is a lot of room for error while installing your own membrane, so do your research). Remember, get the air bubbles out with a drywall knife, but don’t push all the thinset out, have the right trowel size, and overlap seams by 2”! More on reddit.com

I like the Hydroban products. They have premade shower pans, drains, liquid applied and sheet membranes. I normally use the sheet membrane which is similar to kerdi. It is a little more ridgid than kerdi and all of my guys agree that it is easier to install. Local availability might influence you however. We install Hydroban sheet or Kerdi directly over sheetrock. It cuts out us needing sheetrock for part of the bathroom and cement board for the shower. I don't like liquid membranes as much. I think they preform fine, but you have to wait for it to dry to recoat. You should be checking the thickness you are applying at to ensure proper installation if using a liquid membrane. More on reddit.com

Nikwax is the gold standard. I also recommend the wash-in treatment . One important thing to note though is that the waterproof treatment is not actually what makes your jacket waterproof. Instead, its purpose is to cause water to bead up on the outer fabric layer. This is important because if this fabric gets saturated it will prevent the Gore-Tex membrane from breathing and you will get soaked with sweat. The Gore-Tex membrane contains tiny pores that are too small for water droplets to pass through, but plenty big enough for water vapor to pass through. So it's still waterproof whether or not it has a waterproofing coating, it just may not be able to breathe. Anyway, the point of this is to say that if you are getting wet inside your jacket, it's either a result of sweat or a damaged Gore-Tex membrane allowing water to leak in. And if it's the latter, waterproofing spray isn't going to do you much good. Also, waterproof treatments do not last very long at all, especially when applied after the original wears off. Backpack straps and other types of friction make easy work of DWRs, so don't expect it to last long in the field. This is why Gore-Tex is best relied on as a waterproof NON-breathable material. More on reddit.com

There really is no consensus. You're going to find people that insist that kerdi ( either applied fabric membrane over a drywall substrate or the Kerdi boards) is the only way to go and you're going to find people that insist that a membrane such as red guard applied over cement board is the best way to go. I'm a contractor that does many bathroom remodels. And I've used all three of the systems. My personal preference is the red guard applied over cement board. That is how I have been doing showers for many years. I've never had an issue and that's what I'm comfortable with and what I know. And after doing several cost breakdowns between all of the systems I do find that method to be the least expensive which helps lower my cost and maximize my profits. However the other systems are just as effective and work well. My suggestion to you would be to use whatever you feel like will be the easiest for you to work with. More on reddit.com