Fabric decides how little you can carry

These are listed in the order worth acting on, which with travel fabrics is not the order they are usually presented in.

Drying time sets the number you carry

If a garment dries overnight you can carry two and wash one; if it takes two days you need four or five of them. Drying speed depends on how much water the fibre holds inside itself rather than on its surface, so thickness matters less than material. Cotton absorbs water into the fibre and releases it slowly, which is why a cotton shirt washed at night is often still damp at breakfast.

Merino and most synthetics hold water mainly between fibres, where moving air removes it within a few hours. This one property does more to determine bag size than any packing technique, because it multiplies across every category of clothing.

Odour is a chemistry problem

Smell comes from bacteria breaking down residues in sweat rather than from the sweat itself, which is why a garment can smell long after it dried. Wool holds moisture inside the fibre where bacteria struggle to reach it, and its surface chemistry is unfriendly to them. Standard polyester does the opposite: it wicks well but its surface retains skin oils that feed bacteria, so it sours quickly.

On a long trip, treated synthetics reduce this, though such treatments generally wash out over time and the claims are hard to verify from a label. In practice a merino shirt stays wearable for several days and a cheap polyester one is often not wearable twice.

Warmth, weight and bulk are three things

Warmth comes from trapped still air, so a light lofty fleece can be warmer than a heavier dense fabric of the same thickness. Down traps the most air per gram, which is why it compresses so far, and it loses most of that performance when wet. Synthetic insulation is heavier for equivalent warmth but keeps working while damp, and that is the trade you are actually making.

A bag is limited by volume at the gate and by your shoulders on the walk, and those two constraints reward different fabrics. Working out which constraint binds on a particular trip is more useful than buying whatever is lightest on the shelf.

What survives a sink

Anything you plan to wash by hand has to survive being wrung out, which rules out delicate weaves and heavily structured garments. Wool should be pressed inside a towel rather than twisted, because wet wool fibres are weak and lose their shape permanently. Dark colours hide the marks that hand washing leaves behind, and mid-tones hide dust better than either black or white.

On a long trip, a garment that must be dry cleaned is a garment you will carry dirty for the remainder of the trip. Read care labels before a trip rather than at a sink in a room where the only alternative is wearing it again.

Durability and repair

Thin high-performance fabrics buy their weight saving by using less material, and less material means less resistance to abrasion at the shoulders and hips. Rucksack straps wear through light shell fabrics at exactly the points where the load sits, sometimes within a single long walking day.

Seams fail before fabrics on most garments, so reinforced stitching at the crotch, shoulders and pocket corners is worth more than a fibre name. A small roll of fabric repair tape fixes tears well enough to finish a trip and weighs almost nothing in the bag. Choosing slightly heavier fabric for the layer that touches the bag is a sensible trade for the layers underneath it.

Building a set that works together

Pick one fibre family for base layers, one for mid layers and one shell, and the drying and washing routine becomes predictable. Mixing wool and synthetic base layers is fine provided you know which of them can honestly be worn twice.

At the airport, garments sharing a colour family also share a wash load, which matters when a sink can only hold so much at once. The set is right when you can wash any item on any night and still have something to wear the following morning. That test, applied honestly, usually removes two or three garments from a bag before it ever leaves the house.

Everything above, in order of what to do first

1. Drying time sets the number you carry. If a garment dries overnight you can carry two and wash one; if it takes two days you need four or five of them.
2. Odour is a chemistry problem. Smell comes from bacteria breaking down residues in sweat rather than from the sweat itself, which is why a garment can smell long after it dried.
3. Warmth, weight and bulk are three things. Warmth comes from trapped still air, so a light lofty fleece can be warmer than a heavier dense fabric of the same thickness.
4. What survives a sink. Anything you plan to wash by hand has to survive being wrung out, which rules out delicate weaves and heavily structured garments.
5. Durability and repair. Thin high-performance fabrics buy their weight saving by using less material, and less material means less resistance to abrasion at the shoulders and hips.
6. Building a set that works together. Pick one fibre family for base layers, one for mid layers and one shell, and the drying and washing routine becomes predictable.

The takeaway

Choose fabrics by drying time first, odour resistance second, and everything else after that.

Pack for the trip you are actually taking, not the one in the photographs.