Hydro Flask Wide Mouth + Stainless Steel Cap
Silicone is only a gasket/seal — what touches your food is Stainless Steel (304 / 18-8).
Hydro Flask's insulated Wide Mouth bottle set up the plastic-free way - swap the stock plastic Flex Cap for the all-steel Wide Mouth cap and the water path becomes steel plus a single silicone gasket.
The verdict: Silicone only
As it ships, the Wide Mouth pours over a polypropylene Flex Cap - that build would be minimal-contact. Fitted with Hydro Flask's separately-sold Wide Mouth Stainless Steel Cap, the entire water path is 18/8 steel sealed by a single silicone gasket, so nothing plastic sits where you drink. That makes it silicone-only rather than fully plastic-free - but a silicone gasket is effectively the standard for any leakproof bottle; an all-metal seal is rare.
Verification: Manufacturer confirmed · Last reviewed
The Wide Mouth ships with a polypropylene Flex Cap; this all-steel cap is a separate SKU and is what puts the water path in steel.
What it's made of
| Part | Material | Food contact |
|---|---|---|
| bottle body (double-wall insulated) 18/8 (304) food-grade stainless steel | Stainless Steel 304 / 18-8 | Yes primary |
| Flex Cap (stock - replaced by the Steel Cap) ships with — replace Polypropylene screw cap the bottle ships with. | Polypropylene PP, #5 | primary |
| Wide Mouth Stainless Steel Cap (add-on - replaces the stock plastic cap) All-18/8-steel Wide Mouth cap; a separate SKU. | Stainless Steel 304 / 18-8 | Yes primary |
| cap gasket Silicone seal inside the steel cap - the only non-metal part in the water path. | Silicone | Yes seal |
| cap strap steel carry strap on the all-steel cap, exterior | Stainless Steel 304 / 18-8 | No |
A double-wall vacuum-insulated bottle in Hydro Flask's Wide Mouth size. The steel cap screws on and you drink straight from the wide opening - an open-mouth chug cap, no straw or spout, best for plain water. Hydro Flask sells other Wide Mouth lids (straw, flip, the stock Flex Cap), but those are plastic. Comes in a range of sizes and colors, and is about as easy to find as a bottle gets.
Pros
- Excellent insulation and durability on the proven 18/8 steel body
- The all-steel Wide Mouth cap is currently sold - unlike the discontinued Standard Mouth version
- Hydro Flask is about as widely available as bottles get
Cons
- Open-mouth cap only - no straw or spill-proof spout
- The steel cap is a separate purchase, and easy to mis-order (see notes)
Notes
- Beware the lookalike - a Flex Cap sold in a "Stainless" color is still the plastic cap; buy the actual all-steel "Wide Mouth Stainless Steel Cap"
- The all-steel cap fits Wide Mouth bottles only; there is no current all-steel cap for Standard Mouth
- Some users note the silicone gasket can loosen over time
Categories: Water Bottles
Sources
Every material claim above is backed by these. This is the scattered info we centralized.
- manufacturer https://www.hydroflask.com/wide-mouth-stainless-steel-cap Hydro Flask's Wide Mouth Stainless Steel Cap - 18/8 steel; brand states the stainless design keeps water from contacting plastic. Fits all Wide Mouth bottles.
- manufacturer https://www.hydroflask.com/wide-mouth-flex-cap the stock Wide Mouth Flex Cap is polypropylene, and is also offered in a 'Stainless' color that is still plastic
Spot a mistake or something out of date? Let us know — corrections are how this stays accurate.