Good thermal flask

Parents trusts Japanese brands like Tiger or the "Elephant" brand. Personally the one that really lasted from my Uni days till now (like 6 years) with easy-to-wash seamless internal design (no grooves or whatever gap) is Hydroflask. I used it to store hot water for the entire day out. It's like made for sports and outings and school, I bought it during Amazon sale 6 years ago and its still good. Just go check out Takashimaya, Isetan, OG etc. then use your phone to find the product brand and code on Amazon and check out the reviews there before purchasing.