Inside is a glass vacuum thingy to keep the drink warm.
My childhood memory says there's a danger using this kind of thermos if the item has been dropped or the glass broken in any way. So I want to find out if it's safe to use or if it's just a prop for photographs. I also want to know what kind of plastic the lid is made from but there's no triangle on the plastic.
The bottom doesn't unscrew, so I can't remove the glass.
I agree with Thomas: they are either intact, or not, no grey area. Shake it, does it sound like broken glass? Put water into it, can you hear it sloshing anyplace that's not visible? If no, it's intact. The glass is the inner bottle itself, you can look in it, does it look like looking into a jar? Should be all shiny silver in there.
What you remember from childhood warnings was the kids who had milk or something in it, they'd drop it, it would break, but the liquid stayed inside the main bottle, with all the broken glass. Drinking that glass filled milk was very dangerous.
I don't know what kind of plastic those lids are. I looked at mine, it's not one of the soft plastics that have the recycle marks these days, it's a harder plastic, closer to the drinking glasses of the same time period. Personally, I classify mine as probably safe enough. I don't drink out of the cup every day with boiling liquid in it, I use it for a hot liquids carry jar, and almost never even put the cup on it. My standards of good enough might not be yours. I use my stainless steel or pottery cups to drink out of, and just fill them from the thermos.
I remember losing a couple of these to temperature shock, so it might be best to warm it up with warm water before going directly to hot. I remember many more of them falling off kids desks at school and shattering. Definitely no grey area.
Kids would want to open it right away to check, even though there was liquid running everywhere on those that were open a little and the telltale rattle sound on those that were sealed. The teacher would instruct them to leave it so that she would only have to clean up liquid and not broken glass.
I had one featuring the TV show Welcome Back Kotter and another one with Gilligan's Island. Both would be collectible today, but unfortunately they were also knocked off the desk at some point.😢
We have a giant version of that in the Philippines but it is quite durable and not glass inside. It keeps water very hot all day. The idea there, is to get anything to do with heating food and water over with early in the morning so you can ventilate the heat, and then if you want hot water for some reason in the middle of the day, you don't have to heat up your house to get it.
Concur with everybody who recalls that there was never a grey area -- they always shattered when they broke, and made a rattling noise thereafter.
In some models, the protective body is threaded at the top, so you could grasp the opening of the thermos in one hand and twist the body with the other hand until the outer case screws off and you were left with the silvered glass vacuum flask in your hand, permitting inspection.
We still have glass thermos bottles here, I use one every day for my morning liter of warm water, followed by erva maté later (I have a different one for coffee-- the ones I bring with me when I go out are made of stainless steel, but the glass ones are great if I am staying in the house or office). I have broken many of them, and it's always catastrophic. Preheating is a brilliant idea and might keep the thermos around a little longer.