# Why do tea bags float in cold water? **URL:** \ **Category:** Factual Questions\ **Created:** [July 26, 2002, 1:54pm UTC](https://boards.straightdope.com/t/why-do-tea-bags-float-in-cold-water/120932 "2002-07-26T13:54:04Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Morgainelf](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@Morgainelf](https://boards.straightdope.com/u/Morgainelf)\ **Post date:** [July 26, 2002, 1:54pm UTC](https://boards.straightdope.com/t/why-do-tea-bags-float-in-cold-water/120932/1 "2002-07-26T13:54:04Z")
I’ve noticed that when I make tea: If I put the tea bag into cold water, (with the intention of popping the cup in the microwave), the tea bag does not easily absorb water, so floats on top. But, If I put the tea bag into already heated water, it quickly absorbs the water and begins to steep. Why? ---
**Author:** ![Reeder](https://avatars.discourse-cdn.com/v4/letter/r/c6cbf5/32.png) [@Reeder](https://boards.straightdope.com/u/Reeder)\ **Post date:** [July 26, 2002, 2:05pm UTC](https://boards.straightdope.com/t/why-do-tea-bags-float-in-cold-water/120932/2 "2002-07-26T14:05:16Z")
Cold water is more dense than hot water. ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [July 26, 2002, 2:55pm UTC](https://boards.straightdope.com/t/why-do-tea-bags-float-in-cold-water/120932/3 "2002-07-26T14:55:59Z")
I don’t think that the minute difference in density matters much at all. I found [here](http://www.mas.ncl.ac.uk/~sbrooks/book/nish.mit.edu/2006/Textbook/Nodes/chap01/node12.html) a value for the thermal expansion coefficient for water: 1.53 \* 10[sup]-4[/sup] K[sup]-1[/sup]. Assuming that you heat the water 80K, that still only means an expansion of 1.2%, which ought to be negligible. I believe that there’s a mechanical side to it: The tea-bag is made out of some kind of fibre, that probably gets less rigid as it heats up. I believe that the effect of heating up the material to near-boiling will make it a lot more flexible, so that it changes shape and lets out the air bubbles. On a related note: Don’t put in the tea-bag in cold water! The most common misstake when making tea is when people use water that isn’t hot enough. (It’s tempting to say that the most common misstake is to use tea-bags, but it is possible to make half-decent tea with tea bags, if you’ve only got hot enough water, whereas no tea will taste good unless the water is hot.) Try it one day! ---
**Author:** ![Podkayne](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Podkayne](https://boards.straightdope.com/u/Podkayne)\ **Post date:** [July 26, 2002, 3:11pm UTC](https://boards.straightdope.com/t/why-do-tea-bags-float-in-cold-water/120932/4 "2002-07-26T15:11:13Z")
Based entirely on unscientific observations, I would be more inclined to think that it’s the water getting in, rather than the air getting out, that’s the issue. Water absorbed by the tea bag quickly increases its density, so the bag sinks. If the water isn’t absorbed, it floats because the density of dry tea is very low. Does capillary action work better for hotter liquids? And it seems like water moves faster through a material that has already been saturated. Why is that? Am I wrong, and is displaced air the key? As another tea snob, I agree with **Popup**. . . avoid bags! 🙂 But if you have to use them, the best way to make tea with a microwave is to heat the water to boiling in a separate container (like a measuring cup). You might want to consider sticking a coffee stirrer or a toothpick or something in the cup to avoid [superheating](http://www.straightdope.com/classics/a3_111.html). Then pour the boiling water into your cup _pver_ the tea bag. ---
**Author:** ![Morgainelf](https://avatars.discourse-cdn.com/v4/letter/m/71e660/32.png) [@Morgainelf](https://boards.straightdope.com/u/Morgainelf)\ **Post date:** [July 26, 2002, 5:09pm UTC](https://boards.straightdope.com/t/why-do-tea-bags-float-in-cold-water/120932/5 "2002-07-26T17:09:59Z")
Oh, you tea snobs, you’re all alike. 😉 I _know_ how uncouth my tea proclivities are, and I can make a great pot of tea when so inclined. But on occasion I’m just totally lazy. So, more questions raised than answered. Here’s a synopsis of the hypotheses so far (paraphrased): 1. Cold water is more dense than hot water. 2. Flexibility of the bag is affected by heat. The more flexible the bag, the easier water can get in, thus letting air bubbles out. 3. Similar theory, only that the water gets in and saturates the tea so it sinks, rather than sinking because air is released. So, **Podkayne’s** question is in my head too - why is the tea bag more easily saturated when the water is hot? By the way, I’ve tried a search of the Dope’s database for earlier versions of this question. Since we can’t search on three letter terms (tea, bag), I tried teabag. I don’t recommend it. :eek: