Hydro Flask 21 oz Standard Mouth - 24 Hours Cold
Published on 09/22/2026 at 20:51 | Editorial responsibility: Rafael Müller, Editor-in-Chief AD HOC NEWS
Hydro Flask 21 oz Standard Mouth is a stainless-steel insulated water bottle with a 21-fl-oz capacity, a leakproof closed position, and a shape designed to fit most cupholders. Its TempShield double-wall vacuum insulation keeps cold drinks cold for up to 24 hours and hot drinks hot for up to 12 hours.
Capacity And Insulation
The bottle holds 21 fl oz, equivalent to 621 ml. Hydro Flask lists 24 hours of cold-temperature retention and up to 12 hours for hot beverages, with a double-wall vacuum construction.
The 21 oz size sits below Hydro Flask's 24 oz Standard Mouth bottle in capacity. The smaller bottle is a more compact hydration format, while the same category also includes larger Standard Mouth sizes and versions with different caps.
Construction And Care
The bottle uses durable stainless steel, is BPA-free, and is dishwasher safe. Hydro Flask also states that the design preserves taste without flavor transfer and is leakproof when closed.
Its limits are specific: the bottle is not intended for use on a stove, in a microwave, or in a freezer. Hydro Flask also says hot liquids should be kept out of the reach of children.
Price And Position
A US retailer lists the Harbor Blue S21CSX384 model at $34.95 as of 09/22/2026. The same listing identifies the bottle as a 21 oz model with double-wall vacuum insulation, dishwasher-safe construction, and the S21CSX384 model number.
Hydro Flask is a consumer brand owned by Helen of Troy Limited. The US-facing brand operation identifies Steel Technology LLC, doing business as Hydro Flask, at 561 Northwest York Drive in Bend, Oregon.
Best Fit For Daily Carry
The Hydro Flask 21 oz Standard Mouth is a compact insulated stainless-steel bottle for users who want cupholder compatibility, a 21-fl-oz fill size, and long temperature retention. It offers fewer ounces than a 24 oz alternative, but the core insulation rating remains 24 hours cold and 12 hours hot.
Hydro Flask 21 oz Standard Mouth
See the bottle's insulation, care, and compatibility details from Hydro Flask.
Hydro Flask 21 oz Standard Mouth
- Product: Hydro Flask 21 oz Standard Mouth, S21CSX384
- Manufacturer: Steel Technology LLC, doing business as Hydro Flask
- Category: Insulated stainless-steel water bottle
- Capacity: 21 fl oz, 621 ml
- Cold retention: Up to 24 hours
- Hot retention: Up to 12 hours
- Price: $34.95 (as of 09/22/2026)
