Even with mudguards fitted, your legs can get very wet while cycling. As you pedal your legs come close to horizontal from hip to knee, so your thighs get much soggier than they would if you were walking. Rain will also run down your waterproof jacket and onto your upper legs and crotch. It's as clammily unpleasant as it sounds. That's why you need a pair of overtrousers in your commuter bag.

Even with mudguards fitted, your legs can get very wet while cycling. As you pedal your legs come close to horizontal from hip to knee, so your thighs get much soggier than they would if you were walking. Rain will also run down your waterproof jacket and onto your upper legs and crotch. It's as clammily unpleasant as it sounds. That's why you need a pair of overtrousers in your commuter bag.

Probably. There's a couple of alternatives. One is to wear Lycra shorts or cycling tights and change when you get to work. The other is to use a cape, which forms a kind of tent from handlebar to saddle, protecting your legs as well as your upper body. Air can circulate underneath to prevent over-heating.

Assuming you do choose overtrousers, here's what to look for.

Rain protection

'Waterproof' isn't a black and white description. Fabrics are rated on the water pressure that they will withstand. This is measured in millimetres and refers to the height of the narrow column of water that the fabric will support before it seeps through. In the real world, around 5,000mm equates to 'withstands light rain', 10,000mm medium rain, and above that, heavy rain. Note that rain can get in at the seams unless they're sealed. Rain can also run down into your shoes; waterproof socks are a good last line of defence.

Breathability

Most overtrousers are breathable – to an extent. The rating that's sometimes quoted is the amount of water vapour, in grams, that can pass through a square metre of the material in 24 hours. More is better, with 20,000-plus best for higher intensity cycling. Most overtrousers are not as breathable as this, so unless you slow down you will get damp with sweat. You're often best leaving the overtrousers off until it's properly raining. 

Ease of fitting/removal

You'll often put overtrousers on or take them off when you're outside. This will mean getting your shoed feet in and out of the legs. To avoid hopping about, it's import that the lower legs zip open to allow easy access. You'll then be more inclined to take them off or put them on en route too, maximising your rain resistance and minimising overheating.

Cut and fit

Overtrousers are always a bit loose as they have to fit on top of normal trousers. Velcro straps are useful on the ankles and lower legs to cinch them in and stop them catching or rubbing on bits of your bike, particularly the chain. A cycling-specific cut will allow easier pedalling and make it less likely you'll catch the overtrousers on the nose of your saddle when you start and stop. 

Features

Visibility is poorer when it's raining, particularly at night, so reflectivity is useful. Pockets are handy, as are openings that give access to your normal trouser pockets, because it's otherwise awkward to get at keys or a phone. A small pack-size is good because you'll probably carry overtrousers in your bag more than you wear them; it doesn't rain that often.

Here's a selection of overtrousers from across the price range.