cheap ones dont have a propper vacumn in them hence why they fill with water.
My bodum travel press keeps stuff warm for ages and has a sealing lid – like scalding hot for hours as long as the lids shut. – doesnt fit in the berlingo cup holders though. Plus side is it is all metal and doesnt flavor what you put in it (once its all coated in coffee oils 😉 – only chuck it in the dish washer once a month or so rest of time it just gets a quick rinse in hot water .
thermos also has a propper vacumn and keeps stuff hot for ages + has a propper sealing lid and fits in the cup holders.
given up on the cheap ones – they also taste of chemicals.