These tumblers are double walled steel and the strainer insert is removable so that if you would like to use it for coffee or hot chocolate you can. The strainer has a handle to pull it out and pushes in with a small click. To ensure it is inserted correctly, shake the thermos side to side if you do not hear rattling congratulation you did it.
These are also great as the unit has a screw on lid which prevents spills and actually work no more stains on the car seats or wet bags. Once this is removed you can turn it upside down and use it to hold the strainer when you are out and about so no mess is made. These also do not condense staying dry to touch all day. When you want to drink the unit has a press top lid which opens it and allows you to drink from anywhere. Great for when you aren't paying attention to what you are doing so no more spills down your shirt.
When it is time to clean the unit the entire lid separates to ensure you can clean the smallest of tea leaves out from the cap so there is no opportunity for mould or bacteria to grow and hide.