With Warmup Undertile Heating Mat you get a dual core heating element embedded into a tough fibreglass mesh. The wires are prespaced so you don't need to worry about spacing.
Wire Design

Warmup’s Undertile Heating electric element has been approved by the UK's BEAB (British Electrotechnical Approvals Board), America's UL (Underwriters Laboratories) and European equivalents and comes with a LifeTime Warranty and SafetyNet Guarantee. The underfloor heating element has been designed within three criteria in mind.

THIN

We use high-grade insulation materials and production tolerances to ensure that the cable is as thin as possible, so that it will not raise the floor levels.

TOUGH

The high-grade insulation materials and the complete coverage of the earth braid ensures that the heating element, despite being small, is very tough. A stranded conductor is also used to allow for slight lateral movements as the floor settles over time.

SAFE

The cable design has been over-engineered to allow for those accidental knocks that occasionally happen on a construction site. The incorporated ground sheath combined with an RCD, gives complete protection against electric shock in the event of someone drilling though the tiles with the underfloor heater switched on.