Are glass bottles better? 5 big bottle feeding questions answered

There are a lot of steps that go into preparing a bottle. Is all this vigilance necessary? Here’s help if you’re feeling lost.

Are glass bottles better? 5 big bottle feeding questions answered

Photo: iStock/PeopleImages

When my husband and I brought our daughter home from the hospital, our entire condo kitchen quickly became devoted to cleaning, sterilizing and prepping our daughter’s bottles. There was no room left for us to do any meal prep for ourselves—not that we had the time or energy to cook anyway.

Just as we had finished the process: sterilizing the bottle, boiling water, preparing formula, feeding our daughter, and then washing everything, it was time to start all over again. 

Whether you're exclusively using formula, topping up with a bottle, or bottle-feeding expressed breast milk, we’ve got answers to your most common questions. 

Should I exclusively use glass bottles?

As a new parent, you may be wondering if you should choose plastic or glass baby bottles, but the choice really comes down to personal preference, says Janice Heard, a Calgary-based community paediatrician and member of the Canadian Paediatric Society public education and advisory committee.

A recent study published in Nature Food measured the amount of microplastics released by plastic baby bottles, and perhaps not surprisingly, it’s a lot. However, experts say you shouldn’t worry.

These days, parents don't need to be concerned about the quality of the plastic that they're using for baby bottles,” says Heard. "It's very well-regulated." Bottles and liners have been BPA-free since 2012. (If you’re worried, check for the numbers 1, 2, 4 or 5 on the bottom of the bottle, inside the recycling symbol.)

John Boland, a professor of chemistry at Trinity College Dublin and one of the authors of the Nature Food study, agrees parents shouldn't be alarmed by the study's findings. "If you're super concerned about it, then you should use glass bottles," says Boland. “But know that there is no evidence of any adverse outcomes from exposure to these plastics,” he says. 


I had thought it would be important to me that we use glass bottles with my daughter, but after I realized just how many we would need, plastic seemed much more affordable and convenient. 

Michelle Thompson, a mom in Toronto, also switched to plastic after initially using glass bottles. “They’re heavy and I was worried about dropping one in the night and cracking it,” she says. 

When can I stop sterilizing baby bottles?

Once your baby is around four months old, it's no longer necessary to sterilize their bottles, says Marie Tarrant, a professor at the School of Nursing, University of British Columbia Okanagan. Washing them thoroughly with soap and water is perfectly fine, she says.

Four months of age is usually when infants can start putting their fingers and toys in their mouth on their own, too, adds Heard.

Thompson says her daughter was around three months old when she got a little less precious about sterilization. “As long as I always rinsed the bottles immediately after and cleaned them properly, I stopped sterilizing,” she says.


As far as how to sterilize, you’ve got options. Simply adding the bottle parts to boiling water on the stovetop for at least five minutes works well and doesn’t require additional equipment. Or, you may want to invest in a microwave or countertop sterilizer. This option may be a safer bet for mothers who have other children at home, says Tarrant, as it can be put up out of reach and doesn’t leave a pot of boiling water sitting on the stovetop. And while you can certainly wash bottles by hand or in the dishwasher, this method won’t offer proper sterilization due to other dirty dishes or food particles that are inevitable on sponges and in every dishwasher, says Tarrant.

Do you have to boil water for formula? Why can't I use tap water?

If you’re using powder or concentrate formula, it needs to be mixed with sterile water for the first four months, says Tarrant. It’s the best way to ensure water is safe for new babies who are still developing their immune systems. You can boil water for two minutes to sterilize it.

Boiling tap water is important to get rid of things like chlorine or any salts that may be added to city water, explains Heard. If your house uses a well, boiling will reduce the hardness of the water and eliminate any bacteria coliforms that may not affect healthy adults but could be harmful to newborns, she says.

That said, if you’re away from your home or suddenly without electricity—which happened in my case when the power in our condo building went off one weekend—don’t stress about not being able to boil water before mixing it with formula. “For most people living in cities, tap water is very safe and so people shouldn't panic if they have to use tap water for their baby," says Heard. It depends on the quality of the water supply where you live. Because not every community in Canada has access to the same quality of water, the overall health recommendation from experts has to cover all scenarios: to be safe, parents should boil and sterilize the water they mix with formula. “Truly from a public health point of view, the tap water in most cities is safe for an infant to have,” says Heard. “We still suggest boiling it, but that’s mostly to get the chlorine out of it and any salts that are in it. If you have very hard water, then it’s better for the baby not to have super hard water,” she adds.

If you’re on well water and you don’t know 100 percent that there are no coliform bacteria in it, then you absolutely should be boiling the water,” says Heard.

Why shouldn’t I warm up a bottle in the microwave?


It’s important to never microwave a bottle—plastic or glass, says Heard. “Milk doesn’t heat up in a uniform manner [in] and the center of the milk might be really hot.” You could mix it by shaking it and testing it on your wrist, but it’s not recommended, since there is still a risk of scalding the baby’s mouth. Plus, if you’re heating breastmilk, the microwave will also break down immunoglobulins in the milk and change the quality. 

Babies actually don’t need warm milk, but if you do want to warm it up, the safest way is to place it in a container or pot of warm water, or to use a bottle warmer.

In hindsight, I wish we had invested in a bottle warmer when my daughter was young. We usually prepared at least two bottles ahead of time and stored them in the fridge, warming them in a container of warm water when it was time for a feeding (which typically took up to 15 minutes—this is an eternity when your baby is screaming!). I was often anxious about making her wait and I can’t tell you how many times I took the bottle out too early, only to have to put it back in the water because it was still cold. Most bottle warmers are under $100 (new) with many models able to warm a bottle in as little as 90 seconds.

How long will a prepared bottle last out of the fridge? 

After all the sweat, tears, and milk that goes into preparing a bottle, the last thing you want to do is have to dump it. Generally, a prepared but untouched bottle left at room temperature for two to three hours is safe to give to your baby, says Heard. Any longer and it should be disposed of, regardless of whether it was touched or not. (This applies to both formula and breast milk.) 

If your little one doesn’t finish the whole bottle, you should also toss it. “It’s really not good to save that milk and then give it to them later because babies have enzymes in their saliva that will start to break the milk down and contaminate it,” says Heard


When leaving the house with her daughter, Thompson says she would pack her diaper bag with two bottles of sterile water and a separate container of pre-measured formula so that she could mix bottles as needed. “It wasn’t so bad to bring and carry,” she says. “If anything, I felt bottle-feeding gave me more freedom to have help from others, which was key for me.” 

Weekly Newsletter

Keep up with your baby's development, get the latest parenting content and receive special offers from our partners

I understand that I may withdraw my consent at any time.