For years, I have managed not to give puffy coats the time of day on grounds of their shapeless ugliness. Then, blow me down, the other day I realised I wanted one. If that’s not a change of heart equivalent to Jan Moir joining Gay Pride, I don’t know what is.

Admittedly, puffy/duvet coats are exceptionally fashionable at the moment. Junya Watanabe and Gareth Pugh both did slightly bestial-looking (in a positive, beast-affirming way), inflated black ones that could also be pressed into service as dinghies, should you fall into a river. Dolce & Gabbana, Marc Jacobs at Louis Vuitton, Hussein Chalayan and John Galliano reworked the puffy/duvet theme into dresses and skirts. Obviously, the answer to that old question, “Does my bottom look on the enlarged side in this?” would be yes, absolutely, but in a positive, large bottom-affirming way.

However, transient trend factors fade next to the practicalities. Ounce per ounce, they are the warmest coats you can buy. Each year, the bigger brands compete to make them even lighter, so that one day they will be the style equivalent of hydrogen. And the names, from Jil Sander’s fabulous +J Compact Down (left, £79.99 from uniqlo.com) to Patagonia’s Nano Puff, have an adorable, quasi-scientific silliness about them.

What it boils down to is this: when you find yourself about to expire from heat exhaustion on the Tube/bus/John Lewis escalator, you can whip off your nano compact puffy thing and stuff it in your bag. Other advantages, which I hadn’t considered until I stumbled on a discussion on the mumsnet website, is that you can easily wipe baby sick off them. This might seem of relevance only to mumsnet until you consider the wider applications of wipe-down surfaces.

Other pluses: wearing something bulky on top = a slimmer-looking lower half and that sportive-chic (in an Italian, non-participatory way) effect. Minuses include potentially looking like a Sloane, someone who’s given up caring, or a fashion designer played by Ben Stiller. Best, therefore, to avoid pastels.

As for the other traps, pay close attention to proportions. Opt for a cropped one with skirts or dresses, or belt a knee-length one. Other than that, puffy jackets, especially swish ones from labels such as MaxMara, which come in ultra-shiny (or ultra-matte) finishes, are the modern successors to fur. Moncler’s revamped, retro-Seventies shapes, which are all the rage on the (après) ski and Notting Hill scene, come in metallics, wet looks and jersey effects. If you’re concerned about the ethics of using down plucked from live birds, check the label for man-made insulation. The first celebrity who red-carpets her Finisterre (winner of an RSPCA good business award) Primaloft jacket with an evening dress will get major brownie points for being modern and hip. I’m going to stick my neck out and predict it probably won’t be Anna Wintour or Joan Collins.

Notes on puffy coats

Nothing will keep you warmer this winter

Wearing a bulky jacket means slimmer-looking legs

Look out for ethical versions

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