The ThermoSphere Ultimate is a loose-lay electric underfloor heating cable for installation into decoupling membrane mats. It is the first and only cable combining TwistedTwin construction with an in-line joint — eliminating the conventional hot/cold joint that must be recessed into the membrane, transforming installation into a one-step, tool-free process. Achieves 195W/m² at 2-stud spacing or 130W/m² at 3-stud spacing. Cable lengths from 12m to 200m. Rated IP68 and extra heavy use (Robinson Test). Lifetime warranty on registration.
IP68
Protection
In-Line
Joint — No Cuts
195W/m²
2-Stud Output
130W/m²
3-Stud Output
12–200m
Cable Lengths
Lifetime
Warranty
Key Features
In-Line Joint — No Cutting Into the Floor
Conventional cables have a hot/cold joint thicker than the cable body — requiring a groove to be cut into the membrane to accommodate it. Ultimate's in-line joint is the same diameter as the cable throughout — it lies flat in the stud channel with no cutting required, keeping the membrane's waterproofing layer completely intact.
ThermoSphere's proprietary TwistedTwin cable uses a twisted-pair conductor construction that neutralises mechanical stress, preventing the fractures that develop in conventional cables under repeated thermal cycling. A continuous full earth braid runs the entire cable length — making these among the safest electric underfloor heating cables in the UK.
TwistedTwinFull earth braidStress-free
Selectable Output — 195W/m² or 130W/m²
Output is determined by stud spacing in the membrane: 2 studs = 195W/m² (wet rooms and high heat-loss); 3 studs = 130W/m² (primary heating in well-insulated rooms). No tools or accessories needed to change — just vary the routing.
195W/m² or 130W/m²No tools to change
Extra Heavy Use — Robinson Test Rated
Rated for extra heavy use in the Robinson Test — the industry benchmark for cable durability under concentrated loading. Withstands heavy furniture, foot traffic and tile installation without damage.
Extra heavy useRobinson Test rated
Compatible With All Decoupling Membrane Brands
Optimised for ThermoSphere Membrane Mats but compatible with all decoupling membrane brands. Installers with a preferred membrane can retain it while upgrading to the most reliable cable available.
All membrane brandsUniversal
IP68 — Safe in Wet Rooms and Bathrooms
IP68 rated — completely impervious to moisture, safe in wet rooms, shower areas and bathrooms when installed with appropriate accessories.
IP68Wet room safe
Lifetime Warranty — Stays with the Property
Backed by a lifetime warranty when registered online. Uniquely, the warranty transfers with the property on sale — the new owners remain covered.
Lifetime warrantyProperty warranty
Technical Specifications
Technical Data
Voltage
230V / 50Hz
Output (2-stud spacing)
195 W/m²
Output (3-stud spacing)
130 W/m²
Total Thickness
3.5mm
Cable Lengths
12m to 200m
Cable Insulation
FEP and HR-PVC
Protection Rating
IP68
Robinson Test Rating
Extra heavy use
Recommended Max Floor Temperature
27°C (limited by thermostat controls)
Joint Type
In-line (same diameter as cable body — no membrane cuts required)
Warranty
Lifetime (online registration required)
Country of Origin
United Kingdom
ℹ Installation: All electrical connections must be made by a qualified electrician in accordance with BS 7671. Register your product with ThermoSphere online to activate your lifetime warranty.
Frequently Asked Questions
What is the in-line joint and why does it matter?
A conventional cable's hot/cold joint is thicker than the cable — requiring a groove cut into the membrane. The Ultimate's in-line joint is the same diameter throughout — no cutting, waterproofing stays intact, installation time reduced.
Which membrane do I use?
Designed for ThermoSphere Membrane Mats but compatible with all membrane decoupling brands.
What outputs can I achieve?
195W/m² at 2-stud spacing (wet rooms, high heat-loss). 130W/m² at 3-stud spacing (primary heating, well-insulated rooms).
What lengths are available?
12m to 200m. Select based on the area to be heated and desired output.
Can the cable be cut?
No — never cut the heating cable.
Related Products
ThermoSphere Decoupling Membrane Mat
Recommended membrane for this cable
ThermoSphere Peel and Stick Combined Set
Membrane + cable in one kit
ThermoSphere T-MO Thermostat
Smart thermostat
BTU & WATT Calculator
Room Dimensions
Room Type
Living Room
Bedroom
Kitchen
Bathroom
Conservatory
Hallway
Glazing Type
Single Glazed
Double Glazed
Triple Glazed
External Walls
0 Wall
1 Wall
2 Walls
3 Walls
4 Walls
Insulation Level
Poor
Average
Good (New Build)
Required Heating
0
Watts
0
BTUs
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