Thermory in the hands of designers: Frants Seer, KHIS Bathtubs

Everything around us is in constant movement. We cannot stop time and we don’t really need to, but sometimes it stops on its own; in moments when we see something incredible – a wooden bathtub. The creator of the thermally modified wood bathtub, made of Thermory ash, is designer Frants Seer. His idea, which he first came up with for personal use, has now become global and reached hundreds of homes in Europe and America.

“When building our new home we decided to use wood in the bathroom to add warmth and coziness,” explains KHIS co-founder Elin Viiask, talking about their very first wooden bathtub. They liked the idea of a wooden bathtub without a lacquer finish in order to maintain a natural feel. In addition to developing the technology, they also needed the wood to be high quality. Wood is a living material that changes in different environments – it shrinks when dry and expands when wet.

Their search led them to Thermory’s thermally modified wood, which not only provided durability, but also gave the bathtub a luxurious dark brown color. Thermal modification gives wood dimensional stability, which is why it is an excellent choice in exterior design, decking, saunas and heated floors. Thermally modified wood does not absorb water, which means it is mold and mildew resistant. It is natural wood with improved features, including a beautiful rich even tone.

Although the wood they chose is perfect for the KHIS bath, Frants Seer and Elin Viiask often have to debunk myths about wooden bathtubs. Sometimes the myths arise from the belief that lacquer is what makes wood waterproof. Or sometimes people have just bad experience with mass produced bathtubs that are held together by metal hoops, which fall apart quickly and do not hold water after short-term use.

KHIS bathtubs use their own special technology. There are details made of thermally modified wood inside the staves that have been tightened with a cable and the special rubber seals are made according to KHIS profiles in cooperation with Swedish rubber producer Gislaved.

“The first prototype we made with thermally modified wood is still being used by our friends five years later,” says Elin. The second prototype, which launched a home improvement idea into a family enterprise, is still being used in their home today.

“We don’t have a separate shower so the bath gets used as a shower base every day,” adds Elin and admits that the luxurious bathtub has become part of their everyday life. Although sometimes it is nice to light some candles and take time to enjoy the moment. This helps to see the bathtub in a new light. “Perhaps it is even more special to us because we are the ones who created it.”

KHIS bathtubs are a combination of nature and contemporary design. Bathtubs are becoming an important interior design element not only in bathrooms but also in bedrooms and in five years KHIS has produced three different models and made a name for itself.

Designer Frants Seer has numerous ideas for the future. They have already experimented using light teak, which creates a completely different atmosphere than the elegant dark ash. The company is also thinking of designing pedestal sinks with a wooden base to match the bathtub and create a fantastic contrast with the white basin. They are also constantly improving their current bathtub models. “If you are happy with everything then there is no room for improvement,” says the designer.


KHIS bathtubs are assembled by hand; each detail is unique and each bathtub is an exclusive design piece and an engineering achievement. The bottom of the bathtub will be custom made of wood or stone, depending on the client’s preference. The bathtub’s rich chocolate color comes from Thermory ash, which has been processed at 400+°F to ensure water-resistance and durability. Post-processing is done with hot wax. Just like any other bathtub, the wooden tub requires some pampering from time to time. The best thing for this luxurious design piece is to oil and wax it once a month to give it a fresh look.

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