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Should you still wear a base layer in the summer?

Stu Bowers
22 Jul 2021

Should you wear a base layer under your jersey in summer as well as winter? We quiz the experts – and start a heated debate

You’ve seen it on mountain stages of the Giro d'Italia, Tour de France and Vuelta a Espana. As the sun beats down and riders push themselves to their physical limits, they unzip their jerseys. Some reveal an emaciated bare chest; others show off a base layer beneath the jersey.

But who’s got it right? 

When it comes to the question of whether you should wear a base layer under your jersey when the mercury rises, we couldn’t even reach agreement among the few people who work in the Cyclist office, so we decided we needed to investigate the pros and cons more closely.

Logic would suggest that more layers will simply make you hotter in the sunshine, but many will insist that a base layer will actually keep you cooler in the heat.   

Science lesson

The layer of clothing directly in contact with your skin helps your body’s natural defences against overheating. Fabrics must facilitate homeostasis (heat regulation) with adequate moisture management during exercise in hot conditions.

While it’s generally accepted that layered clothing is best to manage your body’s thermoregulation when it’s cold, opinion is divided over whether a base layer should be worn when it’s warm.

‘The type and structure of a base layer needs to change in summer, but the principle remains the same,’ says Graeme Raeburn, lead designer for clothing manufacturer Rapha.

‘Sweat accumulating on your skin needs to be removed – by wicking – to help keep you comfortable and regulate your body temperature. I’d recommend wearing a base layer in all weathers. It’s just a question of choosing the right one for the conditions. 

‘Jersey fabrics might be required to do lots of things – look aesthetically pleasing, be aero, take a sublimation print or embroidery, be dyed to a particular colour and so on – all of which can affect their functionality, but a dedicated next-to-skin layer enables the fabric to target just one thing: wicking sweat, and therefore taking heat away from the body to keep the wearer cool and dry.

'So a purpose-designed summer base layer can be more effective at moving sweat and taking away body heat [than just a jersey] because the structure can have a much bigger surface area for the sweat to evaporate from than bare skin or a more closed jersey fabric.’ 

Omar Visentin, director of R&D at high-end Swiss brand Assos, seems to share Raeburn’s views.

‘In theory, sweat transfer away from the body could be done directly by the outside layer – the jersey – but it is important to realise that this task translates into complex technical requirements for a garment, so a highly specialised textile – the base layer – can have a competitive advantage over a “generalist” garment such as a jersey, which also has other requirements to fulfill.

'That said, there is obviously also room for specific circumstances and personal preferences. Different cyclists might choose different approaches, but I would say that as a general rule the use of a base layer is justified even in hot conditions.’

Not everyone agrees. ‘Anyone who tells you to wear a base layer when it’s hot either a) doesn’t ride a bike, b) is just trying to sell you base layers or c) is grossly misinformed. Actually, it’s probably a combination of all three,’ says Steve Smith, brand manager at Sportful. 

‘To understand when you should wear a base layer it’s good to take a quick look at the physics. When water evaporates, it cools. It’s why your body perspires, so moisture on the skin evaporates and cools it down.

'In cooler temperatures, if that evaporation happens on the skin surface you get cold from the evaporation but also from the conductive cooling of the liquids remaining on the skin if the moisture doesn’t evaporate fast enough.

'That’s why you feel cold in the winter if you’re wet under a jacket and why a 22°C swimming pool feels cold but 22°C air temperature feels comfortable.

'So for cold or moderate temperatures, the goal of a base layer is to keep you dry by moving the moisture away from the skin. When we get to warmer temperatures the goal is to actively cool the body.

'To do this we need to encourage the evaporative cooling and move it as close as possible to the skin. Hence no base layer. We see a lot of pros get this wrong, but it seems like they’re learning now.’

Smith’s argument for ditching the base layer assumes the jersey you’re wearing is itself capable of correctly managing the moisture transition to evaporation.

Of course, Sportful produces a garment designed for this – its Summer Race Jersey. And so as not to start any inter-company squabbling, we looked to an impartial expert. 

Enter Dr Mark Turner of the Performance Clothing Research Group, University of Leeds. He would seem to agree more with Smith than Raeburn and Visentin, although his answer may also surprise you.

When we asked him whether he’d wear a base layer under his jersey on a hot day his response was, ‘No, I’d just wear the base layer.’ 

In a roundabout way this concurs with Smith’s ideal of a single, breathable, wicking layer working best, although it may also conjure up some alarming mental images of cyclists in string vests.

Turner goes on to say, ‘That’s not obviously realistic, more an ideal world scenario. The reality is there are so many other factors to consider with cycling, such as aerodynamics.

'I read once that an “open knit” style [string vest] base layer worn under tight fitting Lycra creates a more aero surface texture [like a golf ball].

I’m not sure if that was ever substantiated, but it goes to show it’s not always just about wicking, especially where pros are involved.

'If a jersey is made in the right way, and has its own wicking properties, I see no reason to wear a base layer. But human physiology is unpredictable and we’re not all alike.

'Everyone sweats at different rates so there’s no hard and fast rule for what will work for you.’ That being the case, we decided to widen the net.

By his own admission, Simon Baynes of sportswear manufacturer Craft is ‘sitting on the fence on this one’. In his opinion it’s entirely dependent on the jersey material.

‘We make a jersey based on the properties of our Cool Mesh Superlight base layer, designed in conjunction with Fabian Cancellara and others, so when the jersey is constructed in this way it’s not necessary to wear an additional wicking layer.’

However he goes on to say, ‘This is a specific case, and I would generally always advise heat management begins with functional underwear – be it summer or winter.’

Comfort matters

Liam Steinbeck makes his living studying fabrics as a material sourcing specialist for Gore Bike Wear.

His opinion is that there is no physiological benefit to wearing a base layer but, like Turner, Steinbeck is clear about one thing – wicking is not the only factor: ‘Even if a garment is engineered for moisture management, if there are poorly placed seams or labels it can be equally negative for the wearer.

'People wear base layers for different reasons – some for comfort, while some believe it helps in a crash.’ 

Rapha’s Raeburn also raises the comfort issue, saying, ‘A base layer can be designed with comfort as the priority, so lighter, softer fabrics can be chosen, flat-locked seams used, and labels placed on the outside. Plus layering bibs over a base layer will be more comfortable.’ 

Andy Storey of cycle clothing retailer Prendas Ciclismo considers another aspect of base layer selection – the right cut.

‘People often ask why they should buy the vest version [of a base layer] when they already have the regular T-shirt shape.

'Limiting the material on the shoulders actually gives a great cooling effect [think about the cycling position] without compromising the extra protection on your chest.’

Storey goes on to say, ‘I always wear a base layer in the UK because the temperature rarely gets over 30°C and when used with a full zip jersey I feel this is the most effective combination.’

Castelli’s senior UK brand manager, Rich Mardle, is also a big believer in the base layer, recounting his experiences riding in South Africa in 40°C+ heat: ‘I found that when I rode without a base layer I felt hotter, especially with hot patches over the shoulders where a jersey alone seemed to retain heat.

'There was noticeably more salt build-up and the comfort wasn’t great. After that I would, and will, always ride with a base layer.’

He does concede, however, that his African adventure was a few years ago and jerseys are now lighter and much more technical. 

So the final answer is… well, there is no final answer. As always, it’s not as simple as right and wrong, and it’s worth experimenting to find what suits you.

Keeping cool, with or without a base layer, will depend on your jersey’s wicking qualities, your comfort preferences and your performance goals.

But most importantly, it will depend on whether you like to rock the Rab C Nesbitt look.

Fit for purpose: Tips on buying a base

Regardless of how technically advanced a base layer is (or how persuasive the sales person), don’t buy one until you’ve tried it on.

It can only function properly if it fits you correctly. By that we mean you need to ditch your sartorial concerns and go skintight – it’s not like anyone is going to see it anyway.

The fabric should hug your every curve without being restrictive to your movements and breathing. It’s important to have as much surface area as possible in contact with your body in order for the material to do its job of transporting moisture away from your skin and allowing the evaporative process to function efficiently. 

Baggy material will not do its job well and will also tend to bunch up under bib-shorts and jerseys, adding to your discomfort instead of making you more comfortable, which is the objective. 

The cut you decide on – short-sleeved or sleeveless – is largely a matter of personal preference, but watch out for tightness under the armpits which can occur with t-shirt-style base layers when you assume the cycling position, especially if you are using a snug fitting jersey too.

This article first appeared in Cyclist Magazine in August 2013.

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