You can store breast milk in glass bottles, BPA-free plastic bottles, breast milk storage bags, silicone bags, or stainless steel containers, as long as they’re clean and food-grade with tight-fitting lids. The CDC recommends glass or plastic containers specifically, and warns against using disposable bottle liners or regular plastic bags not designed for breast milk.
Each option has trade-offs in cost, convenience, and how well it preserves nutrients over time. Here’s what to know about each one.
Glass Bottles
Glass is one of the most reliable options. It doesn’t leach chemicals, holds up to repeated washing and sterilizing, and won’t absorb odors or stain over time. Wide-mouth glass bottles are easiest to fill and clean, and many fit standard breast pump adapters.
The downsides are weight and breakability. Glass bottles take up more freezer space and can crack if you skip one important step: leaving about an inch of empty space at the top before freezing. Breast milk expands as it freezes, and a full glass container can shatter.
BPA-Free Plastic Bottles
Hard plastic bottles are lighter, cheaper, and won’t break if dropped. Look for bottles labeled BPA-free and phthalate-free. These chemicals, once common in plastics, can migrate into liquids over time, especially when heated. Most major breast pump brands now sell collection bottles that double as storage containers and meet these safety standards.
One thing to avoid: warming plastic bottles in the microwave or placing them in boiling water. High heat accelerates the breakdown of plastic. Instead, warm bottles in a bowl of hot (not boiling) water. This protects both the container and the milk, since microwaving creates hot spots that can burn your baby’s mouth.
Breast Milk Storage Bags
Pre-sterilized storage bags are the most space-efficient option, especially for building a freezer stash. They lay flat, stack neatly, and are designed for single use, so there’s no cleaning involved.
Not all bags are equal, though. Thinner bags are more prone to freezer burn and can lead to a loss of fat and antibody content in the stored milk. Choose thicker, BPA-free bags from a reputable brand. Double-bagging or placing bags inside a freezer-safe container can protect against punctures and leaks. Never use regular sandwich bags or disposable bottle liners, which aren’t designed to withstand freezing temperatures or preserve milk safely.
Silicone Bags
Reusable silicone bags are a newer option for parents who want to reduce waste. Food-grade silicone is BPA-free, PVC-free, and phthalate-free. These bags can be sterilized by boiling for 3 to 5 minutes before first use and cleaned with a soft-bristle brush after each use.
Silicone does require more care than disposable bags. Don’t clean it with bleach-based agents or UV sterilizers, both of which can degrade the material. Inspect the bags regularly and replace them at the first sign of damage, since scratches or cracks can harbor bacteria. Store them away from sharp objects and direct sunlight when not in use.
Stainless Steel Containers
Stainless steel is worth considering if you plan to freeze milk for longer periods. A study published in the journal *Breastfeeding Biology* found that stainless steel maintained the most stable nutrient content in frozen breast milk. From the initial freeze through 180 days of storage, there were no significant changes in fat, protein, or carbohydrate levels in stainless steel containers.
The CDC’s official guidance references glass and plastic specifically, so stainless steel occupies a less established spot in the recommendations. But food-grade stainless steel doesn’t leach chemicals, is nearly indestructible, and cleans easily. The main drawback is cost, and the fact that you can’t see the milk level inside without opening the lid.
How Much to Store Per Container
Store milk in the amounts your baby typically eats in a single feeding, usually 2 to 4 ounces. This minimizes waste, since you can’t refreeze thawed breast milk or save leftovers from a feeding. Small portions also thaw faster.
If you’re freezing, always leave about an inch of space at the top of the container. Breast milk expands when frozen, and an overfilled bottle or bag can burst or pop its seal.
Labeling Your Containers
Write the date you expressed the milk on every container before it goes into the fridge or freezer. If your baby is in daycare, add their name as well. Use the oldest milk first. A simple system: place new containers behind older ones so you naturally reach for the earliest date.
Breast milk stays good in the refrigerator for up to 4 days and in a standard freezer for up to 12 months, though using it within 6 months is ideal for quality.
Cleaning Reusable Containers
Wash reusable bottles and containers after every use. The CDC recommends a specific routine: wash your hands first, then take apart all pieces and rinse them under running water. Wash each piece in a clean basin (not directly in the sink, which can harbor bacteria) with hot water, soap, and a brush dedicated to feeding items. Rinse again, then set everything on a clean, unused dish towel or paper towel to air-dry completely.
Don’t rub items dry with a towel. This can transfer germs back onto clean surfaces. Let air do the work.
For babies under 2 months old, born premature, or with weakened immune systems, add a sanitizing step after washing. You can boil items for 5 minutes, use a steam sterilizer, or soak them in a dilute bleach solution (2 teaspoons of unscented bleach per gallon of water) for at least 2 minutes. If you use the bleach method, don’t rinse afterward. The trace amount left behind is safe and breaks down quickly as the items dry.