In reply to Ian Straton:
Hi,
Flysheets on TNF tents are mostly silicon treated on both sides which means they can't be heat taped. The reason for using this treatment rather than a PU coating is that the nylon cannot absorb any water, is slightly stronger (as it hasn't been weakened by the heat taping, stretches less when wet and does not allow snow to stick to it. I think the home sealing job is a small price to pay when you consider the advantages.
Some other manufacturers use PU on the inside and silicon on the outside which is one way round the taping issue. The groundsheets used to be PU coated.....not sure about the current models and I never understood why they aren't taped.