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Short answer: For a preschooler or young grade-schooler, get the 12 oz. It has a push-button lid that covers a silicone straw. For tweens and teens, get the 16 oz. Thermos sizes it for older kids and gives it a push-button spout lid. Both are rated cold for 12 hours and are top-rack dishwasher safe.
How we compare: every spec in this article comes from official manufacturer specifications and product pages (starting with Thermos’s official 12 oz product page and 16 oz product page), all listed under Sources below. We don’t run hands-on tests, and if a spec isn’t published, we say so. Last updated: October 2026.
I live in Japan, where kids carry an insulated bottle to school almost every day. These two FUNtainer sizes are the ones US parents usually choose between.
I haven’t tested these side by side. Everything below comes from the manufacturers’ official product pages, linked at the end. If a spec isn’t published, I say so instead of guessing.
Quick Comparison Table
| Spec | Thermos FUNtainer 12 oz | Thermos FUNtainer 16 oz |
|---|---|---|
| Capacity | 12 oz (350 mL) | 16 oz (475 mL) |
| Height | 6.9 in | 8.4 in |
| Width x depth | 3.1 x 2.7 in | 2.8 x 3.0 in |
| Weight | 0.6 lb | 0.6 lb |
| Cold rating | Up to 12 hours | Up to 12 hours |
| Hot drinks | Not for hot liquids | Not for hot liquids |
| Lid | Push-button lid covering a silicone straw | Push-button spout lid |
| Carry handle | Integrated soft-touch handle | Integrated handle |
| Dishwasher | Top rack only | Top rack only |
| Thermos list price | $16.99 | $18.99 |
| Origin | China | China |
All figures are from Thermos’s US product pages, checked October 2026. List prices are Thermos.com prices, not Amazon prices.
Key differences at a glance
- Drinking style: The 12 oz bottle drinks through a silicone straw, while the 16 oz bottle drinks from a spout.
- Who it’s for: Thermos pitches the 16 oz for older kids, tweens and teens, and the 12 oz has the straw lid that suits younger children.
- Size: The 16 oz is 1.5 inches taller at 8.4 inches but a little slimmer at 2.8 inches wide.
- Price: Thermos lists the 12 oz at $16.99 and the 16 oz at $18.99.
- What stays the same: Both are cold-only, vacuum-insulated stainless bottles rated for 12 hours, weigh 0.6 lb, and go on the top rack of the dishwasher.
The 3 Differences That Matter
1. Straw vs spout
The 12 oz lid flips open to a silicone straw, and the cover protects it when closed. The 16 oz lid opens to a spout, and Thermos says the push button prevents accidental opening in backpacks.
2. Capacity and age
Four extra ounces matter more for a full school day plus practice. Thermos describes the 16 oz as sized for older kids who need more to drink through the day.
3. Shape
The 12 oz is short and slightly wider (6.9 in tall, 3.1 in wide). The 16 oz is taller and slimmer (8.4 in tall, 2.8 in wide), so check the side pocket of the backpack you already have.
What’s the same
Both are double-wall vacuum-insulated, BPA-free stainless bottles with a carry handle, rated to keep drinks cold for up to 12 hours. Neither is meant for hot liquids.
Who Should Buy Which?
Choose the Thermos FUNtainer 12 oz if you:
- Have a preschooler or early grade-schooler
- Want a straw your child already knows how to use
- Want the lower price
Choose the Thermos FUNtainer 16 oz if you:
- Have a tween or teen
- Need more water for sports or long days
- Prefer a spout over a straw
Kids’ Water Bottles in Japan
Japanese kids usually bring a water bottle (suitō) to school, and Thermos Japan sells its own kids’ lineup rather than the FUNtainer. Its cold-only straw bottle FKA-350 holds 0.36 L and is rated at 11 °C or below after 6 hours. Thermos Japan also sells a 0.4 L straw bottle, the FHL-403F.
A Kakaku.com reviewer who bought the FHL-403F for a two-year-old starting preschool praised the capacity, the wide mouth and the easy push button, and noted that replacement parts are easy to buy. They added that it costs more than cheap bottles but is worth it for durability. (Third-party reviews, not our own testing.)
Packing hot lunch too? See Thermos FUNtainer 10 oz vs 16 oz Food Jar.
Thermos FUNtainer 12 oz vs 16 oz Water Bottle: Frequently Asked Questions
Can I put hot drinks in a FUNtainer bottle?
No. Thermos says both bottles are not for hot liquids.
Are FUNtainer bottles dishwasher safe?
Yes, top rack only, according to Thermos.
How long do they keep drinks cold?
Thermos rates both sizes for up to 12 hours cold.
Which size is better for a kindergartner?
The 12 oz, with its covered straw lid. Thermos aims the 16 oz at older kids, tweens and teens.
Check current listings
Prices and colors change often, so check the current listing before buying.
Related comparisons
- Thermos FUNtainer 10 oz vs 16 oz Food Jar: Which Size?
- Zojirushi SW-KA30 vs Thermos FUNtainer 10 oz: Kids’ Jars
- Thermos FUNtainer 16 oz vs Icon 16 oz Food Jar: Which?
- Zojirushi SM-KHE36 vs SM-KHE48: 12 oz or 16 oz Travel Mug?
Sources
- Thermos, 12oz FUNtainer Water Bottle (official): https://thermos.com/products/funtainer-r-water-bottle-12oz
- Thermos, 16oz FUNtainer Water Bottle (official): https://thermos.com/products/funtainer-r-water-bottle-16oz
- Thermos Japan: FKA-350 straw bottle specs (thermos.jp): https://www.thermos.jp/product/detail/fka-350.html
- Kakaku.com: Thermos FHL-403F review (Japanese): https://review.kakaku.com/review/S0000971678/ReviewCD=1955604/
Specs checked October 2026. Prices and availability change, so check the current listing before buying.
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