Timber frames suit some Ayr elevations where the original joinery still reads as part of the stone front. They need painting and careful upkeep in sea air. UPVC frames ask for less routine maintenance and suit many later houses and practical replacements on weathered openings.
On seafront sandstone near the Low Green, style and how the frame meets the wall matter as much as the material name. On later houses in Whitletts, Dalmilling or Kincaidston, low-maintenance frames are often the clearer fit. Neither choice is decided by a website slogan.
A survey sets out options for the openings you want changed. For the UPVC service page, see UPVC windows. For the wider overview, start with Ayr double glazing.