low coeficient for heat
Hmmm.... Presumably you're referring to the coefficient of thermal conductivity? Which is frankly irrelevant, it's a very lower deck device and I sincerely hope that Mrs Pongo wouldn't lower herself to such an item.
The 'Thank you' letter raises great thread possibilities! Years ago, 2 Sqn 4 FTS used to have a 'universal letter' which was excellent - it started something like "Dear (Sir / Mr / Mrs ......) I (have the honour / wish to apologise /would like to thank you) for (your most enjoyable / the use / the abuse / the loan of) (evening / wife / dog / car / daughter)...etc etc with lots of
* delete as applicable notes. It was a true masterpiece - I wonder whether anyone still has a copy?