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Speed up installation with our in-line hot-to-cold joint. Unlike most electric heating cables, there's no bulky joint that needs cutting into the floor. This transforms installation into a one-step process, speeding things up whilst significantly reducing any chance of accidentally damaging the cold tail joint during installation. No cutting also means the membrane’s waterproofing layer stays intact.
ThermoSphere Ultimate® is the ONLY heating cable to combine in-line joint technology with TwistedTwin cable construction. This makes it the most robust 'in-line joint' heating cable you can use. Thats quality for your clients and an easy install for you.


ThermoSphere Ultimate® is compatible with popular heating and decoupling membrane mats. This means you can use your preferred brand of decoupling mat with the easiest to install and most reliable heating cable.
The perfect fit for a bathroom or wet room, the systems advanced waterproofing properties make ThermoSphere Ultimate and membrane a perfect fit. It can be installed up walls as well as on floors and sealed against moitsure by using the ThermoSphere Waterproofing Kit.

With guaranteed reliability there's little to no chance of the cable failing when installed correctly. We're so confident about this that should the underfloor heating system fail in the first twelve months of installation because of a manufacturing fault, we will not only replace the system, we'll also replace the floor covering too*. So, sit back and relax, we've got you covered.
*Available after confirmation of successful warranty registration.
Our in-line joint membrane cables do not have bulky hot/cold joints that are created after the primary manufacturing process. They are the same thickness from the end termination to the cold tail that connects to the thermostat. This makes them stronger, more reliable, and easier to install.
Our in-line joint membrane cables make installation easier because installers don’t have to cut into the membrane, insulation board, or chase out concrete. Cutting and chasing also makes joints the most common point of failure during installation. Removing the bulky joint removes that risk too.
Very. You can simply press the cable into the membrane mat, covering the whole of the heated area, and you’re done. Because there are no bulky joints or thicker cold tail cables, installation is a one-step process. The membrane and cable are automatically flush and ready for tiling.
Material costs are roughly £60–£110 per m² (around £600–£1,100 for a 10 m² area) for ThermoSphere Ultimate & Membrane, excluding labour, insulation, and controls.
It’s the same price, but better cable, so nothing needs to change with the way you work. The only difference is the new product codes have “J” on the end – oh and installation is much easier too, so you’ll spend less time on site.
If you have a question that needs an answer, our comprehensive FAQs page is packed full of them. However, we know that some questions are more complex than others so our team are always available to help.
© 2026 Thermogroup Ltd. ThermoSphere is a trading name of Thermogroup Ltd. Registered in England and Wales (7964492) VAT no. 129420819