Back in 1990 upvc windows were still in there infancy at that time I was working as a rep for Spectus systems who extruded upvc profile which window fabricators then made into finished upvc windows.
Some of the early upvc systems were very bulky and this made the window look hideous The key was for upvc windows to try and replicate the slim sightlines of the then dominant aluminium windows.Spectus had a slim upvc sash called SW14 if I remember correctly this window casement was very slim and the retail boys loved it.But the downside was that it had no eurogroove (a rebated channel for hardware to sit in ) and was really meant for cockspur locking handles.Also if you put an espag(espagnolette) lock it broke through into the glazing chamber(the bit where the glass sits).
upvc windows back then had horrid,horrid thick black gaskets back and front so if you like a thick black rubber line on a white upvc window you were sorted!.The glazing bead was on the outside 99% of the time called externally glazed and had its own rubber that you trimmed to size and a back wedge normally 4-6 mm thick.Some companies did white gaskets these mainly turned yellow.
Glazing thickness was normally 20 or 24mm (24mm) is the optimum air gap for thermal efficency any wider and thermal convections currents form reducing the units efficiency a 28mm unit is 96% as efficient as a 24mm sealed unit and glass was normal float glass without any coatings although you could get something called kappafloat which was the forerunner to K glass.
The spectus upvc window system had a front to back depth of 62mm some upvc profiles there was one called range valley which was 56mm deep and had a honeycomb internal section.You could get upvc windows in mahogany woodgrain foil back in 1990 and on white but that was the only colour choice.
Here are some names of long departed upvc window extruders most had an alarming tendency to turn yellow and failed when they could meet there guarantees others merged or were bought out.
KB sterling ,Gloplas,Home profiles,Diplomat profiles,Goldie,Worth,DLP,Plus Plan,national profiles,Komarek,.
My favourite was Vic,virtually a one man upvc extrusion show who had an extruder and I sold him door sash as he only extruded the window sections I'd love to be able see a window made with his upvc profile 20 years later.