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A new stainless steel bottle you’ll want to take with you wherever you go,

whether commuting or climbing a snowy mountain.

The FLASKER is one of Rivers’ most popular products.
The FLASKER is the first vacuum flask developed by Rivers, and is notable for its design,
which goes against the times by not merely going along with typical cylindrical designs.

However, we have decided that once our current inventory is depleted, we will discontinue the sale of this product. (In fact, our stock is almost completely gone.)
We would have liked to continue selling this product, but are unable to do so due to circumstances out of our control. One year ago, we decided to develop a new flask.
Perhaps it was only natural that we carried on the FLASKER design of our previous product. The fruit of our development work was the new STEM. Because it is a follow-up to a popular product, we worked to make it even better.

Lighter is better
“The lighter a flask, the better its heat and cold insulation properties.”

When people hear this, they are often surprised.

“Isn’t it the other way round?” they ask.

To be sure, vacuum flasks have an image of securely locking in heat behind thick steel walls. The reality, however, is that lighter vacuum flasks work better.

Setting aside technically complex reasons, what could be better than a lightweight flask with superb heat and cold insulation performance?

Let’s compare the weights of our previous product, the FLASKER (420ml), and our new product, the STEM (500ml).


Despite holding 20% more (80ml), it weighs roughly 25% less. So just how light is 200g?

It’s about the weight of a smartphone. High thermo function for overwhelming heat and cold insulation So the STEM was designed to be ultralight, but we didn’t stop there.

We also used all the technologies needed for modern stainless steel development.

One of those technologies was the use of copper plating for the interior of the vacuum compartment. This blocks heat transfer due to thermal radiation, further improving the flask’s heat-retention capabilities.

What is thermal radiation?
Thermal radiation is heat that is conveyed by far-infrared rays.
It is propagated even through spaces with no air. Outer space is a vacuum,
but heat from the Sun is conveyed to the Earth through thermal radiation.

The heat from flask contents also tries to escape through thermal radiation, but copper plating blocks it.

Last winter, we performed a field test. We brought coffee that was freshly brewed in the morning to a snowy mountain in a STEM. In the evening, when we opened the STEM, steam rose out of the top. It is so good at retaining heat that those who can’t handle really hot drinks should probably let them cool a little before pouring them into the STEM.

Resistant to staining, easy to eliminate odors.

The interior stainless steel surfaces of bottles have tiny bumps and indentations, too small to see with the naked eye, that can easily become dirty. STEM is electropolished to create a smooth, gleaming surface. This helps it avoid becoming dirty, and reduces odor buildup from drinks. Customers love how hygienic it is.

Use it as a simple flask or as outdoor gear.
The STEM comes in two designs: a simple standard design and a design with a dedicated strap, called a bottle leash. You can use the bottle leash to hang the STEM from your bag, as a handle when carrying the STEM by hand, or to make it easy to hold when the outer lid is open. Please note that this tremendously useful part cannot be attached to a standard model STEM, so you can’t buy and use a separate leash later.

– Material: Stainless steel (Bottle) / Polypropylene (Lid, Plug)/ Silicone rubber (Lid, Plug)
– Capacity : 500ml
– Thermal insulation effect : 73°C (6hours)
– Cold insulation effect : 7°C (6hours)
– Size : W70mm x D70mm x H225mm
– Weight : 200g
(Not suitable for: microwave, dishwasher, dryer.)

Thieves Coffee is official Authorized Australian Distributor by RIVERS JP

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