There are a huge range of options out there, ranging from £10 to £500 and all claiming slightly different benefits, or claiming the same benefit for vastly different prices. So what do you go for? I'm going to attempt here to give a brief guide, centred around the big question of what the difference is between waterproof and water-resistant.

For something to be labelled as waterproof, it has to pass a universally accepted test where the fabric is put under pressure from a vertical tube gradually filled with more and more water, over a long period of time. The amount of water it can resist is then used to give it a waterproof rating, measured in mm of hydrostatic head (the depth of the water in the tube). In the UK, something is classed as waterproof if it can withstand 1500mm, but for mountain walkers this may not be enough for a wet day.

If you are out for a day in the mountains, you should look for your main waterproof to be rated 5000mm or higher, and most good waterproofs will be around 10,000mm, the highest being around 20,000mm for the wettest conditions. A lower rating means the water will eventually get through if the rain is heavy. Not all jackets have this rating on the shop label, so search for it online before you buy.

This begs the question, what's keeping it waterproof in the first place? The answer for something labelled waterproof is that it has a dedicated waterproof membrane, which has a tight enough construction that water can't get through. This specialist membrane changes between different companies, but many use well known manufacturers such as Gore-Tex or eVent. The membrane is surrounded by other layers of the jacket which protect it and provide other functions such as insulation and durability. A fully waterproof jacket will also have 'taped seams' which prevent water entering via the stitch-marks and zip.

A water-resistant jacket on the other hand does not have a dedicated membrane. It may have a stretchy fabric which helps to prevent light rain for a time, but it is most likely to have been treated with a water-repellant coating which can wear away and which does not withstand heavy rain. The advantages of water-resistant clothing is that they are fine for short walks whilst being cheap, but they should not be used in place of a proper waterproof in the mountains. Something labelled water-resistant would not meet the UK waterproof definition of withstanding 1500mm of hydrostatic head.

Another attribute to look for in a jacket is breathability. This is an indication of how good the jacket is at letting your perspiration out while keeping you dry, to stop sweat building up inside the jacket if you're working hard uphill. A cheaper waterproof may well keep the rain out, but it will probably be worse at keeping you cool, allowing the build-up of moisture inside. A jacket will say if it is breathable and this is important for the warm but wet days of the UK.

Before buying a waterproof or water-resistant jacket, consider the activity you want to do. For full days out in the British mountains or tackling a challenge event such as the Yorkshire Three Peaks, a waterproof is essential as the weather can chance fast, and water soaking quickly through to your skin can cause discomfort, cold and in severe cases can lead to hypothermia through the faster loss of heat when your skin is in contact with a wet surface.

It is perfectly possible to shop around for a waterproof jacket that's good value for money, but don't skimp too much – paying a bit more for a good jacket which will last years and give you the confidence to go out in the rain is money well spent compared to something that constantly lets you down and which you aren't comfortable in.