Long johns occupy an odd position in a wardrobe. They are worn directly against the skin for long stretches, often under two or three other layers, and they are then taken off in the evening and put somewhere to be dealt with later. Nothing about them looks dirty. They come off dry, they show no marks, and a sniff in the first hour suggests they are perfectly fine. By the next morning they are not. The smell that was not there has arrived, and washing them the way you would wash a jumper tends to make matters worse rather than better.
What Actually Smells and Why
Perspiration itself is very close to odourless. What comes out of the skin is mostly water with salts in it, and on its own it would dry off and leave nothing behind but a faint stiffness in the cloth. The smell that develops afterwards comes from the other thing skin produces, which is oil, and from what happens to that oil over the following hours.
Skin oils are large molecules, and large molecules do not evaporate. They sit in the cloth where they landed. Over time they break down into much smaller fragments, chiefly short chain fatty acids, and small molecules evaporate very readily. That is the moment a garment starts to smell, and it is why the smell arrives hours after the garment came off rather than while it was being worn.
This explains something most people have noticed and few have accounted for. A base layer that seemed acceptable in the evening can be unpleasant by morning, and one that has been washed can smell again within an hour of going on. In the second case the oil was never fully removed, only the surface of it, and the rest carried on breaking down underneath.
It also explains why airing works on some garments and not on these. Airing removes volatile compounds that have already formed. It does nothing whatever about the reservoir of oil that keeps producing them, so an aired base layer smells better for an hour and then reverts. The oil itself has to come out, which means detergent and water rather than a windowsill.
Wool and Synthetic Hold It Differently
Merino and polyester both make good base layers and they behave in opposite ways here. Wool fibre has a complex internal structure with a genuinely absorbent core, and odour molecules that find their way into that core are held there and released only slowly. The garment smells less because the smell is locked inside the fibre rather than sitting on its surface.
Polyester has no absorbent interior to speak of. It is a solid, smooth filament, so everything that lands on it stays on the outside, where it is free to evaporate and reach your nose. The same property that makes polyester straightforward to dry also makes it announce every compound that has attached itself to the fibre.
That surface is also a great deal bigger than it looks. Base layer knits are made from very fine yarns, because fine yarn gives a thin fabric that traps air without bulk. Fine yarn means far more individual filaments per gram, and more filaments means far more surface area for oil to attach to. A base layer offers more available surface than a heavy sweatshirt does.
The practical difference lies in what a wash has to achieve. With wool the oil is partly inside the fibre and needs time in the water to work its way out, which argues for a longer soak at a gentle setting. With polyester the oil is on the outside and needs surfactant and a little warmth, which argues for a proper detergent rather than a wool wash.
How Softener Undoes a Base Layer
A base layer does not work by absorbing moisture. It works by moving it, and the mechanism is capillary action. Water in the narrow channels between adjacent filaments is drawn along those channels by surface tension, out towards the face of the fabric where it can evaporate. The knit is essentially a network of very fine tubes.
For capillary action to work, water has to wet the fibre surface. If a droplet beads up on a fibre instead of spreading along it, the channels do nothing and the moisture stays exactly where it is. The whole performance of the garment depends on the fibre surface being something water is willing to spread across.
Fabric softener works by leaving a coating on that surface, and the coating is waxy by design, because wax is what feels soft under the hand. Water will not spread across wax. Once a base layer has been softened a few times, water beads on the fibres instead of travelling along them, and the moisture that should have moved outward stays against the skin.
The knit gets blocked as well. Softener residue accumulates in the spaces between filaments, which are precisely the fine channels the fabric depends on, and a blocked channel carries nothing at all. This is why a softened base layer feels clammy in use, and why it often feels heavier in the hand than it did when it was new.
Dryer sheets do the same thing by a different route, transferring a similar coating by direct contact under heat. If a garment is behaving as though it has been softened and nobody has used any softener, a dryer sheet is almost always the explanation. The effect builds up over many cycles, so the sheet that seemed harmless the first winter is the reason the garment stopped working by the third one.
Where the Stretch Actually Goes
Stretch in a base layer comes from two sources and they fail in different ways. The first is the knit structure. A rib or jersey knit is built from interlocking loops, and a loop can be pulled longer and narrower without the yarn itself stretching at all. A good deal of the give in a garment is geometry rather than elasticity.
That geometric stretch has a limit. Pull past it and yarn is drawn through from the neighbouring loops to make up the length, and that yarn does not travel back where it came from once the tension comes off. The garment has not stretched so much as redistributed itself, and the knee or elbow that was stretched stays baggy.
The second source is elastane, and elastane fails through heat. The polymer softens at temperatures a hot dryer reaches comfortably, and a softened elastic thread held under tension in a tumbling drum takes on a new resting length. This is not gradual wear. One hot cycle can take a noticeable proportion of the recovery out of a garment.
Both failures point in the same direction. Keep the heat down, keep the spin moderate, and avoid hanging a wet base layer from a single peg, because a wet knit is heavy and that weight pulls the loops out of shape exactly as a body would. Lay it flat, or hang it over a line so the load is spread along its length.
A Wash That Keeps Them Working
Turn thermal base layers inside out before they go in. The oil is on the inside surface, because that is the side against the skin, and turning the garment puts the soiled face where water and detergent are moving most. It is a small thing and it makes a measurable difference to how much comes out in a single cycle.
Wash warm rather than hot. Warm water helps the surfactant surround and carry away oil, which cold water struggles to manage, while staying well below the temperature at which elastane starts to relax. Somewhere around a hand warm setting is the useful compromise, and it should be the same setting every time so a set ages evenly.
Use an ordinary detergent and use less of it than instinct suggests. Base layer knits are dense and hold detergent in those same fine channels, and residue left behind attracts soil and stiffens the fabric. An extra rinse does more good than extra detergent, and it deals with the stiffness that people usually try to solve with softener.
Keep them away from towels and heavy cotton. Cotton sheds lint continuously, and lint lodges in a fine knit, where it sits in the channels and does much the same job softener does. Washing thermal base layers as their own load, or alongside other synthetics, is worth the mild inconvenience of a smaller load.
Cold Mornings in Garland
Garland gets a real cold season without getting a long one, which changes how base layers are used. They come out for a few weeks, get worn hard for several days running when the temperature drops, then go back in a drawer for a fortnight when it warms up again. That stop start pattern is harder on them than steady use would be.
The trouble with the gaps is what happens during them. A garment put away with skin oil still in it goes on breaking that oil down while it sits in the drawer, so it comes out smelling worse than it went in even though nothing was done to it. Wash before storing rather than before wearing and the pattern stops being a problem.
The stretch ahead brings the first proper cold and the holidays together, which is when everything gets worn at once and very little gets washed. WaveMAX Garland has the machines for the load that follows, when a fortnight of base layers, jumpers and coats all arrive at the same time.
Before the Cold Sets In
Base layers rarely arrive on their own. They come with the jumpers, the fleeces and the heavy outer layers that have been in storage since spring and smell of it, and all of that is bulky, slow to wet through and awkward in a small drum. Getting it done in one sitting is far easier than spreading it over a week.
The machines at our self-service laundry on Marketplace Drive handle the bulky winter load a domestic drum cannot, and larger drums matter here because a thick knit needs to move freely in plenty of water before detergent will reach the inner face where the oil actually sits.
Our machines and the store are cleaned daily.
Nou wash-dry-fold service covers the everyday laundry.
For general guidance, The American Cleaning Institute publishes a fabric care guide that is a useful cross-check.
The short version
Base layers smell because skin oil sits in the knit and breaks down over hours into small, strongly smelling molecules. Airing removes the smell and leaves the oil behind, so it returns. Wool holds odour inside the fibre and polyester holds it on the surface, so each wants a different wash. Softener coats the fibres in wax, which stops water spreading and ends the wicking. Wash inside out, warm rather than hot, no softener, low heat, and keep them away from cotton lint.
Girland WaveMAX is at 1311 Marketplace Dr, Suite 100, easy to reach from Garland and the surrounding area. If you have a load that will not fit at home, call us at 214-954-7063.