In warmer months, a fleece top may offer adequate insulation for lower overnight temperatures. However, it is less thermally efficient (i.e. less warm for its weight) than down- and synthetic-insulated jackets, which I will discuss later in this series. So I do not consider fleece to be an optimal “stop” piece when backpacking.
Instead, I include a fleece top in my Go Suit for two purposes. It’s a critical part of the Core 13, a 13-item collection of backpacking clothing that can be mixed-and-matched to create appropriate systems for every set of 3-season conditions.
1. Second layer. In cool conditions — e.g. windy summits and peaks, crisp mornings, etc. — a fleece can supplement the warmth (or lack thereof) of my hiking shirt; and,
2. Mid-layer. In cool/cold-and-wet conditions, a fleece serves to increase warmth and to buffer moisture when worn between my hiking shirt and rain shell.
From a physics perspective, fleece reduces both convective and conductive heat loss.
Why not a wind shirt?
A wind shirt made of wind- and water-resistant nylon or polyester like the Patagonia Houdini is a popular alternative as a second layer, since it is lighter and more packable than a fleece. However, a wind shirt is useless as a mid-layer: it does not buffer moisture like fleece, nor does it provide any warmth when wet. In other words, it can only reduce convective heat loss, not conductive. Therefore, I think that the additional few ounces of a fleece is well worth this added role.
That said, I do like wind shirts, but not for backpacking. Instead, I use them for:
- Day-hiking in dry weather, when I may want “low-cost insurance” (i.e. minimal weight and volume) against temporary cold or windy conditions; and,
- Winter runs, when I want an ultralight and ultra-packable shell to reduce convective heat loss, especially early in a run before my body has warmed up.
Fabrics and features
Fleece tops can be made of synthetic fibers (i.e. plastic, specifically polyester or polypropylene) or natural merino wool. Synthetic fleece will be far less expensive and lighter weight for its warmth. It also performs better as a mid-layer because it absorbs less water and dries faster. While I wear a wool fleece top, the Ibex Shak Full-Zip Sweater, nearly everyday in the winter, I don’t think it rivals the field performance of a synthetic.
Mass fleece fabric is available in 100-, 200-, and 300-weight, i.e. the fabric weighs 100 grams per square meter. Higher-grade fleece is usually branded (e.g. Polartec, Patagonia R-series) and sometimes has a grid-like pattern for improved moisture management.
These fabric weights are often categorized as Lightweight, Midweight, and Heavyweight. Lightweight fleece is my go-to. Midweight is best if cold-and-wet conditions are the norm. Heavyweight I would avoid as it’s bulky and more worthy of a standalone jacket, or a mid-layer for winter conditions.
Ironically, for backpacking the best fleece top is the simplest and usually the least expensive option. In fact, it’s the antithesis of the iconic The North Face Denali Hooded Jacket and The North Face Denali Windpro Jacket. Avoid tops with features that only add weight, absorb water, reduce breathability, slow dry times, and add cost — specifically:
- A spandex component in the fabric
- Wind-blocking membranes
- Panels of wind- and water-resistant fabric (e.g. ripstop nylon)
- Lots of pockets and a full zipper
My picks and suggestions
Fleece tops are a commodity item, so focus on fabric weight, features, and price instead of brand. Here are two examples of simple, functional, lightweight, and inexpensive tops made of 100-weight fleece: