This style of stainless steel thermos is commonly found in opshops around Aotearoa (New Zealand) with a broken plastic lid. The lid features a complex and flimsy open/close mechanism which breaks easily (see image below), prompting people to throw the thermos out. The thermos itself is made from high quality stainless steel so we thought it would be good to find some ways of repairing these valuable objects!

This page documents the process of finding various ways to repair the thermos. What we end up with is, I think an improvement on the original design of the thermos lid. It is simpler, more durable and removes the need to have plastic come into contact with the contents of the thermos (which can release BPAs and other chemicals).

I hope that one day we can collect hundreds of these discarded thermoses in a community makerspace and run workshops on repairing them. Contact us if you want to work with us to make it happen!

Method 1:
Order complex flimsy replacement lid from China: Not recommended. Lets find a better way.

Prototype version 1:
Whittle fresh olive branch from garden into stopper using whittling knife: Visually very interesting but liquid easily leaks from the thermos.

Version 2:
Refine olive wood stopper, add bicycle innertube seal and eye hook handle: The wood stopper was designed to sit inside the mouth of the thermos while the innertube seal was large enough to sit over the edge of the lip of the thermos creating a seal. The whole thing was held down with a plastic lid modified from the original (not pictured) with a dremel. Still leaks and combining innertube directly with hot liquid/food is no good.

Version 3:
I try using the lid from a glass jar (cut to size with snips) and fitted inside the original lid with silicone washers. It works, but I think it might rust over time. The aluminium in version 3.5 is a better solution.

Version 3.5:
Aluminium off-cuts and retired food-grade Silicone: Almost there!

Collect retired food-grade silicone from local recycling center. I got mine from the Sustainability Trust (thank you Sustainability Trust, Isabelle Leduc, Polly Griffiths and Kim Tabrum!)

Collect aluminium off-cuts from aluminium supplier. I got mine from Ullrich Aluminium (for $10)

Cut aluminium (using snips) into disk based on the size of the inner diameter of the original thermos lid.

Use dremel to hollow out the original lid – removing the broken open/close mechanism. Insert aluminium disk.

Cut large washers from the food-grade silicone using sharp scissors.

Fit silicone washer and aluminium disk into lid.

Hey presto!¹

This design uses two aluminium disks and three silicone washers. It is actually an improvement on the original design of the lid. It is more durable and removes the need to have plastic come into contact with the contents of the thermos (which can release BPAs and other chemicals).

We are 90% of the way towards a perfect solution. It works well but needs some tweaking, as the silicone and aluminium can fall out if you take off the lid without taking care.

Version 4:
COMING SOON. I have the next version planned. It will use a stainless bolt to keep everything together which I think will solve the problems with version 3. I will post to this page when I have completed it. Join our our newsletter if you want to be kept up to date.

References:
¹ Hey Presto: A phrase announcing the successful completion of a trick, or to suggest that something has been done so easily that it seems to be magic.