What to wear when active in hot weather

cotswold hot weather
cotswold hot weather 2
By Paul Deegan, Cotwold Outdoor, 02 April 2011
Several years ago I attempted to climb Cerro Aconcagua, which at almost 7000 metres is the highest peak in South America. I ignorantly assumed that such a high mountain would require cold-weather clothing from beginning to end. I soon discovered that far from being a frozen landscape, the walk-in involved hiking through a searing hot, wind-blown desert. Enduring temperatures in excess of 30ºC, I ended up sewing a dishwashing cloth to the back of my uncomfortably hot wool cap to keep the sun from scorching my neck.

Ever since that salutary experience, I have always researched my next destination to see what the weather is likely to be during all stages of the journey. More often than not, I’ve discovered that at least some protection from the sun is required. This booklet outlines some of the options for hot weather clothing and equipment in arid, humid, and high altitude climates. 

Protection Factors
The material you wear needs to resist the sun’s rays in order to help delay the onset of sunburn. A lot of clothing is labelled with a protection factor rating. These are similar but not identical to the Sun Protection Factor (SPF) ratings awarded to suncreams. No internationally-recognised measurement standard has been agreed upon for clothing.

However, the Australian Ultraviolet Protection Factor (UPF) has come to the fore. There is also a British Clothing Protection Factor (CPF). Both tests use a spectrophotometer to measure a fabric’s ability to block ultraviolet radiation (UVR). UPF, CPF and SPF ratings are not directly comparable. For example, SPF only measures protection from UVB rays, whereas UPF also takes UVA rays into account.
UPF description:

10 - Less than 10 low (inadequate for UK summer)
20 high protection 10-19 medium
30 & 40 v. high protection 20-29 high
50 max. protection 30+ very high

A garment with a UPF rating of 50 means that 1/50th of the UV radiation falling on the surface is able to pass through. This is equivalent to 98% protection from UVR.

A garment sold without a rating does not necessarily mean that it offers no protection as not all manufacturers submit their fabrics for testing. However, it is not possible to judge how well a fabric resists the sun simply by looking at it. For example, the UK’s Health Protection Agency (HPA) tested a cream coloured, woven 100% cotton fabric which revealed a CPF of just 7. A yellow knitted polyester / Lycra stretch material had a rating of 96. As a general rule of thumb, darker colours resist UV radiation more effectively than lighter colours. The yellow fabric saw its CPF rise to 196 in navy blue.

Despite the extra protection afforded by dark colours, people operating in bright sunlight and hot temperatures often prefer to wear light-coloured clothing. Light colours help to keep you cooler. Pure white often provides higher protection than off-white because white fabrics usually contain fluorescent whitening agents which absorb UVR. White may also be more reflective. A knitted 100% cotton fabric in off-white tested by the HPA revealed a CPF of 9. In white its CPF soared to 57. Special UVA and UVB absorber additives can be washed in to clothing. These can temporarily increase protection.

Ratings can be affected if the material is heavily used, wet, or stretched. An orange
polyester / Lycra knitted fabric saw its CPF collapse from 136 to 35 when the material was stretched by 30 percent. Some cotton fabrics have shown an increase in CPF when wet.

See the ‘Sun hats and suncream’ panel for details of SPF ratings.

In hot and humid conditions some people find that a pure cotton shirt has a tendency to rot and chafe after an extended time, whilst 100% synthetic fabrics that wick sweat rapidly from the skin can feel uncomfortable. By contrast, a durable polyester cotton (polycotton) material that retains some sweat can help to keep the skin cool.

In desert conditions involving high heat and low humidity an all-cotton top works well.
Driving a 4x4 is a different experience to running the Marathon de Sables so the best idea is to research your destination and activity to find out what clothing other people have used. For less extreme, everyday travel in warm conditions, a couple of loose-fitting, soft synthetic shirts that feel like cotton can be ideal as they dry quickly after being washed. The best adventure travel shirts include multiple venting options, a high collar to help keep the sun off the back of the neck, long sleeves to prevent arms from being burnt by the sun, and a long body which enables the shirt to stay tucked in if required. Remember that in high temperatures it is cooler to cover rather than expose your skin.

It is worth remembering that in some countries, baring large areas of flesh by wearing shorts and sleeveless shirts can be offensive to local people, especially around or in places of religious significance. Always have a long sleeved shirt and trouser option in your ensemble.

The same cotton and synthetic fabric guidelines for shirts also apply to legwear, although it is worth bearing in mind that trousers are often subjected to more abuse than a top. If you are heading into rough terrain, such as a dense jungle, a fabric that has a ripstop finish might be worth looking out for. (Ripstop can be identified by the pattern of small rectangular squares visible on the face of the fabric. This reinforced grid helps to prevent small tears in the fabric from continuing across the surface of the material.) Other trousers are reinforced with additional panels of fabric on high-wear areas such as the knees and seat. In the jungle, try to ensure that your trousers are long enough to be tucked inside your boots to deter leeches, or secured over the top of your footwear with durable ankle cords.

More than a few trousers sport zips that run around the thigh. These zips allow the garment to be converted into a pair of shorts. This can reduce the number of individual pieces of clothing you need to carry. Check that the zips do not cause any chafing.

Trouser hip pockets vary in their ability to retain small items on a rough trail. A thigh
pocket can be useful, especially if the contents can be secured with a button or zip.

In addition to a high grade pair of dark sunglasses with wraparound lenses or side pieces to prevents light from creeping in, a popular item of clothing in desert conditions is the shemagh. This large piece of cotton cloth can be used to protect the neck, or wrapped around the face during a sandstorm. When buying your shemagh, make sure it is the real thing as cheap imitations have been found in some souks. In hot and humid climates, a thinner cotton neckerchief is sometimes used to mop sweat from the forehead. The rest of the time it can be worn around the neck to help deter insects from crawling inside the top of the shirt.

A useful piece of equipment in the jungle is a poncho. This waterproof cape can be more practical than a waterproof jacket and trousers because it allows air to circulate around the body. It is worth noting that in humid environments, even the very best waterproof and breathable fabrics are unable to work properly as sweat vapour is likely to condense before it reaches the material. Although this can make it feel as though the jacket is leaking, in reality it is probably sweat beading onto your clothes. When crossing open country in monsoon conditions, an umbrella is one of the best investments you can make.

Some jungle travellers combat chafing and deter leeches by wearing close-fitting, unpadded Lycra shorts, which can be washed and dried on a daily basis. If you are thrashing through a jungle with a machete, a pair of gardening gloves will offer your hands some protection. Ensure that the gloves you use afford a good grip on the handle of the machete.

Experienced jungle explorers make sure that they always have a dry set of clothing to rest and relax in under their shelter at the end of each day, even if this means climbing back into wet clothing the following morning.

To help prevent moisture from damaging your kit, place items in ziplock bags, which in turn go inside small waterproof canoe bags. These bags are then placed in a large
waterproof canoe bag which acts as a rucksack liner. The rucksack liner helps to keep everything dry during river crossings and monsoon downpours, the smaller canoe bags help to prevent things getting wet when the rucksack is being packed and unpacked, and the ziplock bags act as an inner sanctum to help stop damp from migrating between individual items.

Hot environments often demand specialist footwear. For deserts, a boot with a thin suede or canvas upper, a sewn-in tongue and a shock-absorbing sole is ideal for handling both classic sandy and the more usual gravel deserts.

If you are heading for the jungle, wet feet are inevitable. Look for footwear that sports
leech-proof vents. These allow water to easily escape from the inside of the boot. Most people agree that the best jungle boots are made for the U.S. Army. These can be purchased from reputable army surplus stores. (With the exception of boots, military attire is a poor choice when travelling as it can send out the wrong message to authorities and militia with potentially frightening consequences).

Adventure travellers who are passing through hot and dry or humid environments but who are not engaged in expedition-style activities will often find that a lightweight fabric boot or shoe will suffice. A boot that sports an integral waterproof and breathable membrane will prevent water that gets in from escaping and is best avoided. Synthetic and wool or pure wool socks are preferable to cotton blends, which serve only to keep feet damp and prone to blistering.

Experienced jungle travellers pack a pair of lightweight shoes for camp wear in the
evening. Crocs, flip-flops and sandals are useful, but offer little protection from the flora and fauna on the jungle floor if you have to walk around after dark.

Dealing with glacial heat
As I touched on in my introduction, it is not just in classic hot weather destinations that you can be struck down by the effects of heat. Hot weather can take its toll on high mountains too. Nowhere is this more apparent than on glaciers. Trekking across a sun-soaked glacier can feel like an inferno, as the rays are reflected off the white surface and back onto the climber. This explains why mountaineers often suffer from burnt nostrils. One cancer research centre reports that ultraviolet light at 3000 metres is 50% more intense than at sea level, which makes the use of appropriate clothing and suncreams even more critical than at lower elevations.

As in all bright conditions, a pair of dark sunglasses is essential. Cover as much of your skin as possible with high sun protection factor clothing and apply a very high factor suncream on every inch of exposed skin. It is also important to wear a wide-brimmed hat, or a peak cap with a legionnaire-style rear fabric flap. If you’re wearing a helmet, protect your neck with a neckerchief. Mountaineers can do much to avoid the worst of glacial heat and glare by beginning the climb in the early hours. This approach also reduces the chance of having to wallow through treacle-like snow that has been softened by the sun.

Sun hats and suncream
One of the more important items of clothing for any sun-soaked destination is a wide
brimmed sun hat. Check that the brim is capable of throwing the face and neck into
shadow. Venting holes in the crown allow air to circulate freely. A hat can also protect the face from foliage, which can sometimes be sharp enough to scratch the skin. In mosquito country, a head net can be worn over a wide-brimmed hat to keep biting insects away from the face. Wearing any kind of head protection can make you feel hotter, so adjust other layers to remain comfortable.

Some hats roll up to reduce bulk. This feature can be helpful when trekking under a
rainforest canopy, as it allows the hat to be popped into a pocket and brought out when you step into a sun-kissed clearing. However, a hat with this level of flexibility may mean that the brim easily blows up in a wind, increasing the risk of exposure to the sun.

As sunlight passes through the atmosphere, ultraviolet radiation (UVR) is filtered. All UVC and 90% of UVB is absorbed by ozone. UVR that reaches the ground is mainly UVA with some UVB. UVB causes the majority of skin cancers, sunburning and cataracts. UVA is responsible for premature ageing and wrinkling of the skin, and also causes skin cancer.

Suncreams play an important role in helping to reduce the risk of sunburn. Even a wellequipped traveller wearing a long-sleeved shirt, trousers, sun hat and neckerchief will still have some bare skin – notably the hands – exposed to the sun. The ears, lips and nose are also particularly prone to sunburn, and it is these areas that often develop skin cancers.

Reputable suncreams are awarded a Sun Protection Factor (SPF). The SPF is calculated by comparing the difference in the amount of UVR required to produce minimal reddening of skin protected by a suncream to the amount of UVR that’s needed to redden unprotected skin. Using a suncream with an SPF rating of 10 would allow you to stay in the sun for up to ten times longer before burning than had you no cream on. If your skin starts to redden after 15 minutes, a factor 10 cream will protect you for up to two and a half hours. It is important to recognise that smearing on additional cream after the protection time has elapsed makes no difference at all. Try to stay out of direct sunlight between late morning and mid-afternoon when the sun is at its most potent.

SPFs only gauge the level of protection from UVB. Protection from UVA is sometimes indicated with a multi-star system, although there is no international standard to label the degree of protection from UVA. It’s always preferable to choose a suncream that offers a high level of protection (high SPF and maximum stars) from both types of UV radiation.

Repelling insects
Many insects are particularly active between dusk and dawn. They include the female Anopheline mosquito which transmits malaria and some other nasty infections. If you are active at this time, a long-sleeved shirt with collar, trousers, socks, shoes and a headnet are all essential. Some jungle travellers have found that mosquitos can be particularly attracted to dark clothing. Applying liberal amounts of an appropriate insect repellent to any remaining areas of exposed skin is very important.

Specialist travel clothing impregnated with a wash-resistant repellent is now available. An alternative to buying dedicated insect repellent apparel is to impregnate your existing garments with permethrin. Before applying a repellent to a fabric check the label on the bottle to see if it damages any materials you may be wearing, and test on an unimportant area of the garment such as a hem.

Other insects, such as the Aedes mosquito which transmits Dengue fever and yellow fever, bite during the day. Investigating the destination you are intending to visit before departure will enable you to know not only what to wear but also when to wear it. If you think you will be entering a region noted for its biting insects then take time to find out from your travel clinic or GP which prophylactic medicine (such as for malaria) or inoculations (such as for yellow fever) are required.

People who suffer anaphylactic shock when stung by an insect such as a bee may require an immediate injection of adrenaline. Talk to your GP before departure about your specific requirements and whether you should pack an EpiPen.

Watch The Knowledge videos online at www.cotswoldoutdoor.com/theknowledge

This guide is part of the series from The Knowledge and you can read more from this series within The Active Guide or alternatively watch The Knowledge videos online at http://www.cotswoldoutdoor.com/theknowledge.

Paul is the author of the award-winning ‘The Mountain Traveller’s Handbook’, and is under licence to Cotswold Outdoor Ltd.

With special thanks to Corrin Adshead for his advice on gear for jungle expeditions, and Mark Gillett for his guidance on clothing and equipment for desert journeys.

© Outdoor Industries Association 2018

OIA Ltd, EICA Ratho, South Platt Hill, Newbridge, Edinburgh, EH28 8AA


+44 131 333 4414