Hi,
I work for an electrical heating company and we are currently working on heating mats and cables for Aquariums, Well I say 'We', I really mean me as a side project. The heating mat is made of silicone, with a Nickel Chrome element fused between layers of Silicone sheet in the case of the cable the element wire is covered with a silicone rubber sheath which is vulcanised to the element. I have contacted our supplier to see if the silicone that we are using is Aquarium safe. I would have thought so because some of these mats and cables are used in a food environment, obvioulsy I cant say too much but one of the High Street burger chains is a customer of ours for both Mats and Cables. If anyone is really interested I will post any updates to the project as I find them.
Rich