[jstanley]

OK, my mistake. To me, a tape measure is a steel thing that coils itself up. Let's try and find some numbers for cloth and plastic:

https://www.engineeringtoolbox.com/linear-expansion-coeffici...

ABS heats up by a factor of 100e-6 per degree C. The largest number I spotted was paraffin with 106e-6 to 480e-6 per degree C.

If the tape measure is made of the most-expanding type of paraffin, which is itself the most-expanding material listed, then the 100mm measurement becomes 100.05mm when heated by 100 degrees C. I really don't think a difference of 50 micrometres matters, or is even achievable, in the manufacture of a bra.

EDIT: (But I see the other points now - it's not the thermal expansion of the tape, but the body's reaction to the temperature).

[jschwartzi]

Intercostal muscle tension probably has a bigger effect than thermal expansion of the tape. The intercostals are the muscles that control how close together your ribs are. They're auxilliary muscles for breathing. Diaphragm and core muscle tension will also have an effect. Your pectoralis muscles and trapezius and deltoids will all also have an effect. These are all muscles that control the size and shape of your ribcage. The human body is not a static shell, but flexes and changes shape depending on the tension of different muscles.

When we touch cold things to our skin, we naturally tense up. If your intercostals, diaphragm, and core are tense when you're being fitted for something that is snug against your chest, then when you get it out of the box it will be too tight.

[diminoten]

> To me, a tape measure is a steel thing that coils itself up.

So like, when you're talking about or to someone on a topic where you're not even sure about the basics like, "what kind of tape measure do they use?" I would urge you strongly to go into "information gathering" mode, rather than "correct perceived incorrectness" mode.