LUCID Premium Waterproof Mattress Protector, Queen Size – Fitted Sheet Style, Machine Washable – Cotton Terry Top Cover – Dorm Room Essential – White

I use one of these: https://www.amazon.com/dp/B00A2G9VFM I've never actually tested it by pouring milk over it. I got it because I'm wary of insects, being a man who travels around a bit. Of course, if you are folding your mattress up every morning, that's not an option. It would only work if you leave it down.