Start With a Strong Base: A Guide to Thermals

4 mins

The humble thermal is where every adventure begins. Unfortunately, it often gets overlooked. But choosing the right type of thermal for your activity is critical for comfortable (and warm) adventures. Here’s everything you need to know about your most essential layer.

What’s the purpose of a thermal base layer?

A base layer is your first layer of clothing; it sits directly on your skin and forms the foundation of your layering system. The main purpose of base layers is to help manage moisture. Base layers aren’t just limited to underwear either; now you can find everything from long sleeve tops and long johns to camisoles, singlets and tees. At Macpac, we have two kinds of thermal base layers – merino and synthetic.

Merino Thermals

Our merino thermals are available in a range of fabric weights, from 150 g/m² through to 220 g/m² styles and are ideal for year-round comfort and versatility in warm or cool climates. Merino yarn is super fine, lightweight and soft on skin — without being itchy or heavy like traditional wool.

Key benefits of merino include:

  • Naturally temperature regulating
  • Naturally odour resistant
  • Comfortable and non-itch

Synthetic Thermals


Prothermals are our premium synthetic thermal option, made from Polartec® Power Grid™. Designed for superior breathability, maximum warmth, and weight reduction, Prothermals are an awesome option for technical performance during high-output activities such as climbing or hiking.

Key benefits of Prothermals include:

  • Lightweight and compressible
  • Maximum warmth-to-weight ratio
  • Breathable
  • Moisture wicking
  • Odour control technology


Exothermals are an excellent all-rounder made from Polartec® Power Dry® which is an advanced next-to-skin moisture-wicking fabric. Designed as a performance base layer, Exothermals can be worn on adventures in all weather conditions.

Key benefits of Exothermals include:

  • Lightweight
  • Moisture-wicking
  • Highly breathable and fast to dry
  • Odour control technology


Geothermals are our ‘entry-level’ synthetic thermal. Made from polyester that contains recycled content, Geothermals are a great option for all-round performance and warmth during activity.

Key benefits of Geothermals include:

  • Durable fabric construction
  • Moisture wicking
  • Breathable and fast to dry

Quality thermals will last you a long time, so think of them as an investment in your adventure kit.

Some call it nature's wonder fibre, and for good reason. Discover why and what makes it different from other wools here.
We've put together a guide to what you should be looking for in your layering system. Check it out here.
5 minutes
Whether you just want to keep cosy or you're after high performance, here are a few things you should consider.