Fakro's windows are great. Can't say the same about their online information. Not only do they not have a product selector or matrix with all options but they also tease you with details, only for you to find out it's a limited selection. They readily admitted that their website is clunky and that people usually just get frustrated and phone them up.

If you're a self-builder who tries to get these things done on weeknights and weekends it's a nightmare (we just ripped our roof off today to realise there's a 3 week lead-in time to get the correct flashing kit.

So...

There are four pieces to a Fakro:
1. Flashing kit (e.g. EZV)
2. Underfelt collar (XDS)
2. Window (e.g. FTT U5)
3. Airtightness collar for inside (XDP)

Make sure you get the XDS and XDP, unless you're sure you really don't need them.

The type of window you get will depend on the pitch of your roof and the flashing kit will depend on the roofing material (and window).

Don't be fooled by websites telling you the EHV Thermo is a "universal" flashing and "can be used with all types of roof coverings". The EHV is for *high profiled* roofing. It is not universal and not designed to work with plain clay or slate tiles for example. (The second letter in their flashing codes refers to the roofing material and the third letter refers to the level the window is installed into the roof.)
http://www.roofingsuperstore.co.uk/product/ehvat05-fakro-single-universal-flashing-with-additional-thermal-insulation-78cm-x-98cm.html
http://www.phstore.co.uk/ehv-at-thermo-flashing.html

If you want a Thermo flashing choose the flashing type you need based on your window and your roof material and then simply append "Thermo". (apart from the EPJ, there's no thermo version of that.)