Hydro Flask 21 oz Standard Mouth with Flex Cap
Hydro Flask
21 oz Standard Mouth Insulated Bottle with Flex Cap
Steel where it matters most, plastic only in the cap, plus a trade-in program and published materials disclosure. One of the cleaner mainstream bottles.
A double-wall vacuum insulated stainless steel bottle you drink from steel, not plastic. The Flex Cap is the one plastic part; Hydro Flask publishes a materials disclosure and runs a trade-in program.
How this score breaks down
Strengths
- Drink path is stainless steel, not plastic
- 24 hours cold and 12 hours hot without any plastic liner
- Trade-in program takes back used bottles
- Publishes a California AB1200 required materials disclosure
- Replacement caps sold separately, extending service life
Trade-offs
- Flex Cap is plastic and touches the water at the threads and gasket
- Cap resin type is not named on the product page
- Colored exteriors are powder-coated; the interior stays bare steel
Scored on our durable-goods method (durables-v1, 2026-07-03). How we rank →
What's inside
Durable stainless steel body with TempShield double-wall vacuum insulation, leakproof when closed, dishwasher safe. You drink from the steel mouth; the screw-on Flex Cap is plastic with a flexible strap. Stated BPA-free; the cap resin is not specified on the product page. Not for stove, microwave, or freezer use.
Free of BPA (stated); plastic in the bottle body or insulation
- Packaging
- Not stated
- Microplastics
- Low. Drinking contact is steel; the plastic cap touches water at the threads and gasket. Rigid plastic, minimal abrasion in normal use.
Attributes
What this product is, at a glance.
Certifications
None listed. We only show independent third-party certifications we can verify with the issuing body, and this product does not currently hold any.
About Hydro Flask
Hydro Flask, part of Helen of Troy, popularized the insulated steel water bottle. It publishes a California AB1200 materials disclosure and runs a bottle trade-in program, which is more end-of-life responsibility than most drinkware brands show.
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