Are Plastic Thermos Safe?

There’s no doubt that having a plastic thermos with steaming hot coffee on a cold winter’s day is great. However, with the discovery of microplastics, you could be forgiven for being concerned about your plastic thermos’ safety.

Whether plastic thermoses are safe depends on many factors, especially what plastic it is made of. Heat and age are the main causes of chemical leaching. BPA-free plastics are not necessarily safe because their alternatives are also hazardous. Plastic is also bad for the environment.

So, if you want to know whether you should ditch your plastic thermos or not, read on!

Are BPA-Free Plastics Safe?

BPA-free plastics have been seen as the way to go for around a decade now. But what is BPA? Bisphenol A is a chemical widely denounced as a carcinogen and may be an endocrine disruptor. So, besides causing cancer, it can also disrupt your hormones.

BPA can affect the timing of puberty, increase body fat, decrease fertility and affect the nervous and immune systems. It’s safe to say that it’s really not a good thing.

So, BPA-free is one way to ensure safer plastics. But does this ensure safety overall?

The alternatives to BPA, including BPS (bisphenol S), have been found by studies at the University of Missouri unsafe. BPS having been tested on animals, it was found that synthetic chemicals like BPS can penetrate through a mouse’s placenta and could do the same in humans.

A similar study conducted at Washington State University examined the effects of BPA alternatives, like BPS, BPF, and BPAF. These alternatives were found to have almost the same results as BPS itself and the same basic chemical structure.

Therefore, if you thought BPA-free was completely safe, think again. Even BPA-free plastics leach chemicals that are endocrine disruptors.

Are Plastic Thermos Toxic?

Although plastic thermoses are affordable, light to carry, and usually dishwasher safe, it cannot be overlooked that there is a risk of leaching chemicals. This leaching is exacerbated by exposure to higher heat.

Leaching also occurs after machine washing, as one study conducted at the University of Copenhagen found. Washing your thermoses in your dishwasher increases leaching as the heat from the washing wears down the plastic.

The heat from microwaves is also not preferable. Putting your plastic thermos in the microwave might cause the plastic to break down so that you are ingesting microplastics. These microplastics might negatively impact your health.

The words “microwave safe” are an assurance that the container will not melt in the microwave, but this does not mean your plastic is safeguarded from leaching if you microwave it.

Different Types Of Plastic

You should also check for the recycling codes at the bottom of your thermos. Types of plastic to avoid include code 3 (phthalates), code 6 (styrene), and code 7 (bisphenols). The latter category can be fine if you see that it is biobased, which means it is made from corn.

However, this is just a general guideline. Unfortunately, most products are mixed, and although you might be able to tell what the major plastics used are, you won’t be the wiser when it comes to the ancillary plastics.

Bottles labeled with codes 2 (High-Density Polyethylene), 4 (Low-Density Polyethylene), and 5 (Polypropylene) are generally considered safer. A problem with these types is they often smell and stain after a while. However, they are cheaper and do not have as much of a problem with leaching chemicals.

Phthalates are particularly dangerous as they have been linked to a higher risk of blood pressure and diabetes in children and teens and a higher risk of miscarriage in women. They are an artificial chemical that helps make plastics more difficult to break.

How Often Should I Replace My Plastic Thermos?

Plastic water bottles need to be replaced at least once a year. Age is another factor that causes the leaching of chemicals.

It would be best if you replaced your bottle, irrespective of the type when there is a persistent smell you can’t get rid of. If the bottle has started to crack, you should replace it; this is a breeding ground for bacteria. Additionally, if the lid or mouthpiece becomes difficult to clean, it’s time for a new bottle.

It would be best if you ideally cleaned your bottle after every use. This is because a build-up of bacteria can occur otherwise. A good way to thoroughly cleanse your bottle of odors and bacteria before you decide to replace your bottle is by soaking your bottle in a mixture of one part water and one part baking soda.

Alternative To Plastic Thermos

Despite being more expensive than plastic thermoses and heavier to carry, metal thermoses offer superior insulation than plastic and are far less likely to leach chemicals. Additionally, metal thermoses have the bonus of maintaining temperatures even longer.

However, be sure to avoid rubber and plastic lids insofar as possible, as you will just end up with the same problem!

Other alternatives to plastic include glass and porcelain.

Other Considerations

A regular stainless-steel bottle releases fourteen times more greenhouse gases and makes use of seven times the fossil fuels of a plastic bottle.

Although a stainless-steel bottle’s initial fossil fuel contribution is higher than that of a plastic bottle, plastic bottles are more often chucked out than metal ones. This is often because plastic bottles get damaged or start giving off a funny taste.

Therefore, if you use your stainless-steel bottle repeatedly, in the long run, it’s going to be better for the environment than the countless plastic bottles you keep throwing away.

Similarly, glass bottles are also more sustainable and safer in the long term, although they have a greater chance of breaking, so they cannot necessarily be used for as long as stainless-steel bottles.

Glass can be recycled. Stainless steel is fully recyclable! However, plastic usually has very low recycling rates and often ends up in landfills.

Plastic bottles can crack when dropped, but stainless steel is by far the most durable, only denting at worst when dropped.


Plastic thermoses are generally quite unsafe, especially when exposed to heat and left over time to break down. Stainless steel thermoses are a much better alternative for the environment and health. If you still want plastic thermoses, you should replace them regularly.


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