Hydro Flask Standard Mouth 21oz 621ml - 24 Hours Cold

Hydro Flask Standard Mouth 21oz 621ml is a stainless steel insulated water bottle with a compact profile and a cap that seals when closed. Its narrow opening and cupholder-friendly shape give the bottle a focused role between small everyday bottles and larger wide-mouth containers.

Core Specifications

The bottle holds 21 oz and uses TempShield double-wall vacuum insulation. Hydro Flask rates the model for cold drinks for up to 24 hours and hot drinks for up to 12 hours.

The construction uses stainless steel, and the bottle is BPA-free and dishwasher safe. Hydro Flask also lists a leakproof-when-closed cap, pure taste with no flavor transfer, and compatibility with most cupholders.

Cap And Daily Handling

The Standard Mouth opening is narrower than Hydro Flask's Wide Mouth design, while the listed 21 oz capacity keeps the bottle below the brand's larger 32 oz formats. The cap must be closed to provide the stated leakproof performance.

Hydro Flask says the bottle should not be used on a stove, in a microwave, or in a freezer. Hot liquids also need to be kept out of children's reach, making the care instructions part of the product's operating limits.

Price And Category Context

A Walmart listing for the black 21 oz Standard Mouth with Flex Cap showed $32.95 (as of 09/23/2026). The listing identifies one bottle and gives dimensions of 3.25 x 3.25 x 10.00 inches.

Compared with a 32 oz Wide Mouth bottle, the 21 oz Standard Mouth offers a smaller stated capacity and a narrower opening. Compared with an uninsulated bottle, its defining distinction is temperature retention rather than a larger fill volume.

Best Fit And Limits

The 21 oz Standard Mouth is a reusable insulated water bottle for users who want a 21 oz capacity, most-cupholder compatibility, dishwasher-safe care, and cold retention rated at 24 hours. Its smaller capacity suits shorter hydration windows than larger bottle formats.

The practical verdict is specific: choose this format for a compact insulated bottle with a narrow mouth and a screw-closed cap. Its limits are the 21 oz capacity, the need to close the cap for leakproof performance, and the prohibition against stove, microwave, and freezer use.