Retention hours only compare when the stated conditions match
Every vacuum flask on the shelf claims the same physics — a double-wall vacuum between two skins of stainless steel, usually published as 18/8 — so the useful differences are elsewhere. Makers publish hot and cold retention times in hours, and each figure comes from conditions the maker sets: a starting temperature, an ambient temperature, and a threshold that still counts as hot. Two flasks quoting the same duration have not necessarily been measured the same way, which is why the conditions matter more than the hours do. The mouth diameter is the specification that decides daily use. A narrow mouth pours cleanly and loses less heat; a wide mouth takes ice, a bottle brush and soup. The lid is both the part that leaks and the part that fails. A plain screw stopper has nothing to break; a push-button or flip lid is easier one-handed and hides a gasket that has to come out and dry. It is worth checking whether the maker sells replacement seals, because a flask usually outlives its first gasket by years. Then the outside: a powder coat resists chipping and adds grip, bare steel shows every knock, and the base diameter decides whether it stands in a car cup holder at all. We compare stated capacity, wall construction and steel grade, published hot and cold retention times with the conditions given, mouth diameter, lid type and seal availability, base diameter, finish, and empty weight.
500 ml · double-walled stated · leak-proof lid · no retention hours published · no steel grade named
A 500 ml double-walled stainless flask that publishes its capacity and nothing else the category is compared on: no retention hours, no steel grade, no mouth, no weight.
Best for: A day bag where 500 ml of double-walled stainless steel is the whole requirement and the hours are not being compared.
≈ $8
32 oz · double wall vacuum · 18/8 stainless · 12 h hot and 24 h cold stated · narrow mouth · carabiner straw lid · hand wash only, stated in capitals · will not stand in a cup holder
The narrow-mouth Iron Flask, which pours cleanly and will not take a bottle brush — and the only listing on this shelf whose maker rules out the dishwasher outright.
Best for: Someone who pours rather than scoops, and does not mind washing by hand
≈ $9
500 ml · vacuum insulated · SUS 201 outside and SUS 304 inside · 24 h cold and 12 h hot stated · brushed finish · top handle
The only flask here that names a different steel for the inside and the outside, alongside a stated vacuum, both retention figures and a brushed finish.
Best for: A day out where a named inner steel, a stated vacuum and a dishwasher-safe body matter more than the hours quoted.
18/8 stainless · double wall · 24 h cold and 12 h hot stated · three lids supplied · powder coat · capacity not published
The flask with three lids in the box and both retention figures on the page — and no capacity anywhere in the listing, which is an unusual thing to leave out.
Best for: A walker who wants a straw lid on the trail and a plain lid at work, from one flask.
1 liter · five-layer vacuum insulation stated · 12 h hot and 24 h cold stated · leak-proof with carbonated drinks · scratch-resistant surface
The only flask here that publishes a layer count for its insulation — five — alongside both retention figures, and that never describes the closure holding it all in.
Best for: A liter where the construction claim is what is being bought, and the closure is being taken on trust.
1 liter · double-wall vacuum · 18/8 stainless · 24 h cold and 12 h hot stated · wide mouth stated to take ice · screw lid with vacuum seal
A 1 liter vacuum flask with a wide mouth stated to take ice, a screw lid with a vacuum seal, a carry handle and a non-slip silicone base — and no dimension behind any of it.
Best for: A liter of iced drink where a wide mouth and a dishwasher-safe lid matter more than packing small.
≈ $22
1 liter · double-walled stated · 18/08 stainless · tea infuser supplied · "several hours" and no figure · 60-day money-back offer
A 1 liter flask with a removable tea infuser and a named steel, whose retention claim is the words "several hours" and no number at all.
Best for: A liter of tea brewed in the flask, where the infuser matters more than a published number of hours.
500 ml (17 oz) · double-wall vacuum · 18/8 stainless · 24 h cold and 12 h hot stated · screw cap · cotton sleeve supplied
A 500 ml (17 oz) vacuum flask in 18/8 steel, 12 h hot and 24 h cold stated, with a cotton sleeve; no weight published and no US seller right now.
Best for: A commute or a day walk where a sleeve and a plain screw cap suit better than a straw or a flip lid.
0.75 liter · double-walled stated · 24 h cold stated, no hot figure · rubberized screw stopper · leak-proof with carbonated drinks
A 0.75 liter flask that publishes a cold figure and no hot one, and whose rubberized screw stopper is stated to hold carbonated drinks.
Best for: Cold drinks, including carbonated ones, in a slim 0.75 liter bottle where the closure is the deciding part.
8 oz · TriMax triple insulation, the only triple-wall claim here · food-grade stainless, grade not named · 24 h stated once, hot and cold not separated · removable 3 oz silicone cup · folding hidden handle · dishwasher safe, flask and cup
The only triple-wall claim on this shelf, on an eight-ounce flask with a removable three-ounce silicone cup in its base — and a single 24-hour figure that does not separate hot from cold.
Best for: A hip-pocket flask for spirits or a single coffee, where two can share from one cup
≈ $10
40 oz · vacuum insulated · food-grade stainless, grade not named · 12 h hot and 24 h cold stated · wide mouth, stated to take ice · straw, chug and handle lids · matte powder coat · twelve dollars
Three lids — straw, twist spout and carry handle — on a forty-ounce wide-mouth bottle with a matte powder coat, for twelve dollars.
Best for: A gym bag and a car boot both, where one bottle has to be a straw bottle, a pour bottle and a carry bottle
≈ $12
32 oz · double-layer vacuum · 18/8 of 304 stainless, the only AISI number here · 12 h hot and 24 h cold stated · wide mouth · straw lid and leak-proof spout lid · silicone boot supplied · powder coat · lifetime warranty
The only listing in this group to name the AISI number behind 18/8 — 304 — with two lids split by use, a silicone base boot and a limited lifetime warranty.
Best for: A bottle that will get knocked about, where a base boot and a named steel grade are worth more than a third lid
≈ $20
16 oz · vacuum insulated · 18/8 stainless · 18 h hot, the longest on this shelf · 24 h cold · twist-and-pour stopper · built-in serving cup · dishwasher safe, top rack · matte steel
Eighteen hours hot is the longest retention claim on this shelf, on the one listing here that combines a twist-and-pour stopper, a built-in serving cup and a dishwasher.
Best for: Coffee or soup carried overnight and poured into a cup, where hot hours are the whole point
≈ $26
1 liter · 18/08 stainless · 13 h temperature stability stated, hot and cold not separated · bottle brush, jute bag and carabiner supplied
A 1 liter flask supplied with a natural-bristle brush and a carabiner, whose single retention figure of 13 hours is never split into hot and cold.
Best for: A liter bottle bought with its brush and its carry loop, where cleaning matters more than a comparable hours figure.
≈ $33
This family belongs to the cooking and water kit — see everything that has to work with it.
Hot retention is published with its conditions. Read alone, it compares to nothing.
Thermos SK2000MSTRI4 Stainless King vacuum-insulated bottle, 16 oz
Capacity decides the number of cups, and it is what sets the weight once full.
Cold retention is a separate figure, given on its own because it does not follow from the first.
With the retention conditions stated beside it: starting temperature, outside temperature, flask full or not.
The number of walls and whether there is a vacuum between them. That is what makes the insulation.
It is published and describes corrosion resistance. It explains part of the price spread.
Because hot and cold do not behave the same way. Both are published separately.
It offers more exchange surface at the opening. The published figures apply to the actual model.
Intended uses are in the maker’s manual. This site reports them without extending them.
Washing instructions come from the maker, particularly about dishwashers. Nothing is prescribed here.
It depends on the model and on the spares offered. The lid type is published on every entry.
A retention figure is only worth the conditions published with it. The rest is settled at the mouth and the lid — the two places where heat and leaks get out.
The table keeps only what four items in five declare. A half-empty column hands an advantage to whoever kept quiet.
| Model | Price | Capacity | Wall construction |
|---|---|---|---|
| Mont-Clair MOSTA6301 | $8 | 500 ml — stated in the title | Double-walled insulation — stated; the listing does not use the word vacuum |
| IRON °FLASK 32 oz narrow mouth water bottle with straw lid | $9 | 32 oz — stated, about 950 ml. The maker’s own wide-mouth listing states that only its 14, 18 and 22 oz versions fit a car cup holder, so a 32 oz bottle from this range does not | Double wall insulation — stated, and credited with keeping the outside sweat-free with cold drinks. No vacuum is named in so many words, and no layer count beyond two |
| EcoVessel 8 oz insulated flask with removable shot cup | $10 | 8 oz — stated, about 240 ml, with a separate 3 oz silicone cup that fits into the base. It is the smallest capacity on this shelf by a wide margin, where the rest run from 16 to 40 oz and the European side reaches a liter | TriMax triple insulation — stated by name. It is the only triple-wall claim on this shelf; every other listing here states a double wall, and this shelf's introduction opens on the assumption that the physics is shared. No layer materials are described |
| Fanhaw 40 oz insulated water bottle with three lids | $12 | 40 oz — stated, about 1.18 liters. The listing adds that 18, 24, 32, 40 and 64 oz versions exist, which confirms that capacity is a variant of one listing in this category rather than a separate product | Advanced vacuum insulation — stated, with no layer count. The word vacuum is used, which two listings on this shelf avoid |
| honogo de-straw-29h-159 powder-coated 32 oz flask, two lids | $20 | 32 oz — stated, about 950 ml, and stated in both the title and the bullets | Double-layered vacuum insulation — stated, with the bottle described as 100 per cent sweat free and free of condensation |
| magcheer WBSW | $22 | 1 liter — stated in the title | Double-wall vacuum insulation — stated |
| Thermos SK2000MSTRI4 Stainless King vacuum-insulated bottle, 16 oz | $26 | 16 oz — stated, about 470 ml, described as compact. The maker states that the Stainless King also comes in 40 oz and 68 oz. It is the second-smallest capacity in this group | Vacuum insulation — stated as the maker’s own technology, with the exterior stated to stay cool to the touch with hot drinks and sweat-free with cold. No layer count beyond the vacuum |
| Blockhütte BH0013 | $33 | 1 liter — stated in the title | Not published on the listing — the flask is called insulated throughout, and neither a double wall nor a vacuum is named |
| Arendo A307177x1 | — | 500 ml — stated | Double stainless shell with vacuum insulation — stated; also stated to be safe with carbonated drinks |
| IRON °FLASK St_24Black | — | Not published on the listing — the listing names 12 oz, 16 oz, 20 oz and 24 oz as the sizes that fit a cup holder, without saying which size this reference is | Double wall insulation — stated; the listing does not use the word vacuum |
| Limes 8 Thermosflasche | — | 1 liter — stated in the title | Five-layer vacuum insulation — stated; no other listing in this hub publishes a layer count |
| NORDMUT BTL-STS | — | 1 liter — stated in the title | Double-walled insulation — stated; the listing does not use the word vacuum |
| Nuactiv | — | 500 ml (16.9 fl oz) — stated | Double-wall vacuum insulation — stated, and stated to reduce condensation on the outside |
| THERMOcafé by THERMOS 4067205075 | — | 0.75 liters (25.4 fl oz) — stated in the title | Double-walled — stated; the listing does not use the word vacuum |
$8 – $9
2 models
Mont-Clair MOSTA6301, IRON °FLASK 32 oz narrow mouth water bottle with straw lid
$10 – $12
2 models
EcoVessel 8 oz insulated flask with removable shot cup, Fanhaw 40 oz insulated water bottle with three lids
Specifications: manufacturer sheets for camping and hiking gear and the matching Amazon product pages. Prices and availability: Keepa. Every figure in this table names its source.
Most recent revision in this category: October 23, 2026.
Prices in these summaries were read on the dates each review gives. The live figure sits beside every product.
