Every year like clockwork, as the impending doom of being steamed alive in a navy suit sets in, I start fielding questions about hot weather fabrics. I’ve found that there seems to be a lopsided understanding of which fabrics are appropriate for warm weather. Almost everyone seems to know that linen is a summer fabric, but most people also believe cotton is a good option while wool isn’t.
Regardless of the season, when choosing a suit fabric, relative warmth isn’t the only concern. Other factors such as weight, hand (feel of fabric), drape, content, durability, weave, and color all contribute to the decision-making process. In this post, I focus on the qualities that affect a fabric’s relative warmth to help you make an informed choice for your next summer suit.
Most men’s suits are made of one or more of the following fibers:
Linen is made from the cellulosic vegetal portion of the flax plant. It’s very durable and susceptible to wrinkling, for better or worse.
Cotton is harvested from the soft, fibrous cellulosic boll that encases the seeds of the cotton plant. It’s the most widely used natural fabric in the world.
Wool comes from the hair of sheep from various species. It’s by far the most common men’s suit, sport coat, and trouser textile.
Mohair is similar to wool, however the hair comes from the Angora goat. It’s courser than wool, but has very good memory (wrinkle resistance).
Silk is an extraordinarily long and fine fiber secreted by silkworms to create cocoons. It has luxuriously high luster.
Polyester is a manmade polymer (plastic) fiber. It’s very durable and wrinkle resistant.
There are several properties that affect how a fabric will perform in the heat. Some of them are fairly intuitive, such as openness of weave and thickness, but other factors are less perceptible.
How easily air moves through a fabric is a big factor in its relative warmth as it affects whether warm air stays close to the skin or if it can easily escape. The thickness of the fabric and openness of the weave have a clear effect on air permeability, but if we compare fabrics of similar weight and weave (see chart below), it becomes apparent that some fabrics are inherently more breathable than others.
From the chart we can see that wool and mohair are the most breathable, which might strike many as counterintuitive, since they are generally considered to be warmer materials. Lighter weight (sometimes called tropical wool) and smooth finished wool are processed differently than winter weight wool in that the fibers have been aligned and twisted together during the combing and worsting processes. The result is straighter fibers with less crimp and fuzz, which helps eliminate the microscopic air pockets that exist in heavier wools, such as flannel and tweed. These air pockets function as mini insulators by trapping air and limiting permeability, thus keeping the wearer (human, sheep, or goat) warm.
Though linen and cotton are both cellulose-based plant fibers, we can see that cotton is less permeable. When people ask about cotton for summer suits and jackets, I generally ask if they’d wear a denim jacket in August, which normally helps drive home my point. In my experience, the thickness and weave of cotton makes a big difference in its breathability, so the thicker it is, the more stifling it becomes. This is why a cotton dress shirt doesn’t seem particularly hot.
Silk is seldom used on its own in suits these days, however it isn’t particularly breathable. It’s generally used in blends with linen or wool in very open weaved fabrics and is normally added for aesthetic purposes.
Polyester is without a doubt the worst option for summer (…or fall, winter, and spring for that matter). It’s essentially a plastic fiber and as most people know, plastic is by definition non-permeable, which makes it a great choice for things like keeping your ketchup in the bottle or preserving your 1973 living room sofa. Just to be clear – don’t buy a polyester suit.
It’s hard to find quantifiable data on moisture retention/dissipation, or how it relates to warmth, but I can say with certainty that wool is very good at wicking away moisture and cotton is horrendous. If you’ve ever tried to peel off a drenched cotton t-shirt, you know how clingy it is. However, moisture retention on its own doesn’t seem to paint the whole picture. For instance, linen can retain a similar amount of water as cotton without feeling as wet.
Being protein based fibers, wool, mohair, and silk are all hydrophobic, but in their woven state they too can become saturated with water. How a fabric reacts at different levels of saturation is also a bit nebulous. I combed through all the scientific research that I could find, and in the end, decided that there were too many conflicting conclusions and factors that needed to be controlled for to make a meaningful chart for moisture retention/wicking and how it relates to warmth. You’ll just have to take my word that wool and mohair are very good at not retaining sweat and cotton is very poor. In my experience, wool clothing rarely needs to be cleaned due to sweat while cotton dress shirts get smelly quickly.
Though it’s not a factor most people would ever think about, each fiber has a different thermal conductivity, which can be thought of as how easily a material absorbs and dissipates heat. It’s the reason we don’t drink hot coffee out of uninsulated metal cups – it would burn our hands initially before quickly cooling to room temperature. The inverse, how well a material resists thermal conductivity, is referred to as the R-Value, which is also the rating given to the pink fiberglass batting used to insulate the exterior walls of buildings.
In the chart above we can see that the plant-based fibers offer the most thermal conductivity. Though cotton scored low marks on air permeability and moisture retention, it does offer some solace from the heat in its ability to transfer warmth away from the skin. However, linen offers a similar degree of conductivity while scoring higher in the other categories, so overall it is still the preferred plant based fiber for thermal conductivity, all other factors being the same.
Wool and mohair are relatively poor conductors, which is why a bulky wool sweater is much warmer than its cotton counterpart. Silk scores a little better on conductivity than it did in air permeability, but it doesn’t stand out as particular good or bad in either category. As with all of the other warmth retention factors, polyester is horrible. Don’t buy polyester.
So then, what’s the best summer fabric? Linen is a great option, but not always dressy enough. The commonly held notion that cotton performs well in summer is not that accurate, so I don’t usually suggest it as a stand-in, especially since it doesn’t tailor well at weights light enough to consider for warm weather. I’m of the opinion that an open weave, tropical weight wool or mohair suit is every bit as cool as linen without the sacrifice of excessive wrinkling, so that’s usually my recommendation. Don’t buy polyester.