Tissue factoids:
John, by getting model aircraft covering tissue you purchased high wet strength - which is important if you like to cover "wet" ie making the tissue moist before covering, laying it over the structure reasonably straight and glueing or doping into position. The tissue shrinks firmly as it dries so it covers tightly.
There are indeed different weights of aircraft tissue (or at least there used to be) "lightweight" and "heavyweight", and these are still available, but take more searching for.
If anyone wishes to cover "dry" then florists tissue, or the packs that come from stationers will do the trick, although they are not very strong.
5 Star make a wide variety of covering tissues (Starspan) in at least 2 weights
http://www.starspan.co.uk/Mike Woodhouse supplies a large variety of coverings - including polyester and carbon fibre tissues
http://www.freeflightsupplies.co.uk/look under "LW coverings" (btw Jap tissue means high quality, high wet strength tissue with one side glossy - normally very lightweight)
hope this may help somebody
andrew
stick and tissue freak