I often like to pack a hot flask of coffee, tea, or soup to take with me on my outdoor adventures.
Usually I'll opt for an insulated Hydro Flask or something similar but I've been loving my Nalgene bottles lately and I know they can handle fairly high heats.
That let me to wonder whether or not it's safe to warm up things in a Nalgene bottle in the microwave.
You can microwave Nalgene bottles as they are made from Tritan plastic which is BPA and BPS free and can handle high heats. However, it's difficult to microwave things inside a Nalgene as the bottles are quite tall and you should ideally only microwave items with the lid off to prevent the build up of steam.
Very few microwaves are tall enough to place a Nalgene bottle in them standing up with their lid off. So generally speaking it's better to heat up drinks or food in a separate container and the pour into your Nalgene once it's hot. Nalgene bottles can handle boiling temperatures – but some chemical leaching is possible (though yet unknown).
Since Nalgene bottles are made of plastic, there’s also a worry that they might melt in the microwave—but fortunately, most of Nalgene’s products (with the exception of the Ultralite model) are designed to withstand temperatures higher than a microwave’s interior.
You should NOT microwave stainless steel Nalgene bottles as the steel will get hot which can melt the lid and your drink inside will warm up very slowly.
Also, Nalgene bottles made before 2008 shouldn’t be microwaved as they contain a harmful chemical, BPA, which is prone to leaching into drinks when it’s heated up.
Nalgene’s FAQs aren’t specific on the safety of microwaving their bottles (probably because it's quite rare for people to consider doing this).
It’s apparently safe to put their bottles in a hot dishwasher, which I do regularly—but how about putting them in a microwave that works on high levels of heat and radiation?
Ultimately, it depends on what model of Nalgene bottle you have, as well as your compliance with some safety precautions. Microwaving your Nalgene could be a good option, but usually there are other much better options for heating up drinks or food.
Is it Safe to Microwave Nalgene Bottles?
If you have a Nalgene bottle made before 2008, it’s highly likely that microwaving it will leach harmful chemicals. Back then, Nalgene bottles contained BPA, a chemical that leaches more readily when heated and can cause serious health issues.
Conversely, you can safely microwave a Nalgene bottle made after 2008: that year, Nalgene switched to a new, safer material that doesn’t leach and that many users report microwaving without issues.
There’s also the risk of a Nalgene bottle deforming or melting in the microwave, but that shouldn’t happen with most models.
Most Nalgene bottles are made to withstand very high temperatures up to 230°F/110ºC or higher—which is higher than water will boil at in a Nalgene.
That said, watch out if you have the Nalgene Ultralite model! The softening point of those bottles is only 153°F/67ºC, so you might experience some interesting results if you put one in the microwave (my friend’s melted and had to be thrown away!)
Below you can see the effect boiling water had on my Ultralite Nalgene. It makes it suuuuper soft.
The Ultralite bottle eventually bounced back to it's usual shape, but it's definitely concerning and I think it could easily be permanently warped if you use it in the microwave because some areas of the bottle could heat up beyond 212ºF/100ºC.
According to comment on this forum microwaving your Nalgene to heat water to make a Nalgene hot water bottle or for a cold hike is something that quite a few people have done with success.
The key here is you need to be very careful with it and check it frequently to avoid disaster.
Here are some quotes from that forum:
I put my nalgenes in the microwave when ever I am heading off for a cold weather hike.Paradox
I've nuked water in HDPE Nalgenes frequently. Yeah, it softens the plastic; it burns your hand getting it into the cozy; and once it starts to cool the side may cave in, but I haven't seen any permanent damage.
EDIT: I should mention; this has usually been in microwaves too small for the Nalgene to stand upright, so I close the lid and nuke it on its side…stopping and checking frequently to hopefully avoid superheating.jniehof
Is It Safe To Microwave Stainless Steel Nalgene Bottles?
While it's fairly safe to microwave plastic Nalgene bottles (made after 2008) stainless steel bottles are a different story.
While you can put stainless steel Nalgene bottles in the microwave and they won't spark it's generally not a good thing to do.
Stainless steel reflects microwave radiation and can become extremely hot in the microwave. If you have the lid on then the heat from the stainless steel bottle can potentially melt or warp the lid of your Nalgene.
Because the stainless steel Nalgene bottles are quite tall you would need to lie them on the side with their lid on to microwave them – risking melting the lid.
While I haven't tested this with a Nalgene I did put my Hydro Flask in the microwave and ended up damaging the lid.
To heat up water in a stainless steel Hydro Flask bottle simply remove the lid and you can boil water on a stove or on a campfire.
Alternative, heat water in the microwave in a microwave safe container and then pour directly into your Nalgene bottle.