French term (edited): calo = calorifugeage

The term you need depends what this is: on pipes, 'lagging' might be more common, but not on other things; it may also depend on what form it takes: some of the modern 'rigid' types may have special names.
Do be careful, though, as that 'hors' is a trap for the unwary — sometimes it can mean 'without' (cf. HT) — i.e. the diamater of the pipe itself, without counting the lagging; BUT sometimes it can mean 'outside', as in 'dimensions hors tout' = 'overall dimensions' etc. So you may need to look carefully at the figures given in order to confirm which it is!