Choosing a borosilicate glass or BPA-free water tank

The Ratio Eight encompasses the daring pursuit of great coffee while utilizing some of the best materials known to the market, creating a harmonious balance of form & function. The water tank in the Ratio Eight holds cold water before it is sent to the heating element, and it is available in two different materials. Whichever material you choose, the Ratio Eight will brew in exactly the same way.

Please note that ALL Ratio Eight models ship with a borosilicate glass carafe, regardless of whether you choose a glass or BPA-free water tank.



The first option is a handblown borosilicate glass tank. It takes a lot of skill and time to produce this part. A small team of lab-grade glassmakers must fabricate multiple weld-points with  fastidious attention to tolerance, all achieved with hand tools. It took us nearly a year of trial-and-error before we came to our final product, which has a gorgeous flow and feel, adding the last note of elegance that ties the entire unit together. You will notice very slight undulations in the glass, as it was at one point a liquid that was annealed slowly to form the water tank. 

Here’s a short video that we produced a few years back when we were still dialing in all of the processes with our factory partners:


Our second option for the water tank is a BPA-free co-polymer,  which captures nearly the same level of optical clarity when side-by-side with its handblown glass counterpart. A few Ratio owners have remarked to us how similar to glass it looks when placed on their countertop.

As the glass tank is made by artisans and is a very time-consuming process, the co-polymer tank is made in large batches with minimal human finishing required to produce the perfect part. This allows a significant cost reduction, which is why the glass tank option comes along with a surcharge.  

With our goal to use absolutely the minimum amount of plastic parts, your Ratio Eight will come with handblown glass internal lines regardless of your water tank material choice. Additionally, no heat is ever applied anywhere on the tank. This means that your BPA-free co-polymer tank is never exposed to any step other than cold water transfer, serving its function without any subsequent exposure to hot water.


 A note regarding tank markings:

The BPA-free copolymer water tank has water markings for full (8 cups) and half (4 cups), with accuracy to within 1 ounce. The glass water tank has the same markings, but due to the handblown nature of glass have a variance of 2-3 ounces. Both tanks hold 44 ounces / 1.3 liters of water at the full mark, with roughly 10% of that volume absorbed into the coffee grounds. 44 ounces poured into the water tank should yield about 40 ounces of brewed coffee. Some "first run" Ratio Eight units built in 2015 (and reviewed by some media outlets) had tank markings AND carafe markings that were not close enough for accurate brewing. Tank markings were made more precise on units built after 2016, and markings were removed from the glass carafes.

Whichever tank material you choose, you can look forward to a beautiful coffee routine and possibly the best cup of coffee you’ve ever made.

As always, if you have any questions we are an email away at [email protected].