Bottles and Thermoses for School: What Capacity | Picasita

Bottles and thermoses for school

The bottle is the heaviest thing a child carries in their backpack and the item most often lost. Here’s how much capacity they need by age and which material works best in each case.

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By Javi · Updated: 2026-07-27

A thermos is a double-walled stainless steel bottle with a vacuum between the two layers, which keeps the temperature for hours. A regular bottle has a single wall: it weighs less and costs less, but doesn’t keep cold or heat.

The weight nobody counts when packing the backpack

Half a liter of water weighs half a kilo. If the guideline is that a 25 kg child shouldn’t carry more than 2.5 kg, a full bottle already takes up a fifth of the weight budget, and that’s before adding a single book.

That’s why we recommend 350 ml for toddlers instead of 500. The child doesn’t drink less: they refill at the playground fountain.

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Why it works

Stainless steel for the thermos

Double wall with vacuum chamber. Keeps temperature for hours and doesn’t transfer flavors, which is the usual downside of reused plastic.

Silicone for the little ones

Lightweight and doesn’t dent when dropped, which happens daily with toddlers. The silicone allows laser engraving, so the name is marked directly on the material.

Capacity adjusted to age

350 ml for toddlers, 500 ml from primary school onwards. More capacity isn’t better if the child ends up carrying weight they don’t drink.

Suitable for food contact

They comply with regulation EC 1935/2004, which governs materials that come into contact with food and drink.

Comparison

Steel (thermos) Silicone Character bottle
Maintains temperature Yes, hours No No
Weight empty High Low Low
Drop resistant Dents easily Yes Yes
Name engraving allowed Yes, laser Yes, laser No, it’s resale

Frequently asked questions

How many milliliters does a preschool child need?

350 ml is the best size for ages 3 to 6. It weighs half a kilo less than a full liter and there’s always a place to refill at school.

Does the thermos keep cold all school day?

Double-walled steel thermoses keep temperature for hours, enough for a school day. Exact duration depends on how many times it’s opened: each opening renews the air inside.

Can the name be engraved on the bottle?

For the steel and silicone ones in our own catalog, yes, with laser engraving on the material itself. Character bottles are official resale products and are not personalized.

Can they be put in the dishwasher?

Silicone holds up well. Steel thermoses are better washed by hand: the dishwasher’s hot cycle can affect the vacuum seal over time, which is what insulates.

Are they suitable for hot liquids?

Steel thermoses yes. Silicone bottles and character bottles are designed for water and cold drinks.

Less capacity, less weight

Choose the milliliters by age, not by what fits in the side slot.

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