Winter dressing in Australia can be unpredictable. Crisp coastal mornings, chilly offices, sunny afternoons, all in one day. That’s exactly why thermal underwear is such a smart investment.

But here’s the key: layering only works when it feels invisible. The goal isn’t to pile on clothing. It’s to create warmth, comfort and a smooth silhouette using the right base layers.

If you’ve ever avoided thermals because you’re worried about bulk, this guide is for you.

Why Thermal Underwear Is the Smartest Winter Base Layer

Think of thermal underwear as your foundation layer, the piece that quietly regulates body temperature without demanding attention.

A well-designed thermal top or thermal bottom works by:

• Trapping warmth close to the skin (heat retention)
• Supporting natural temperature control between indoors and outdoors
• Reducing the need for thick outer layers
• Allowing freedom of movement throughout the day

The difference between bulky layering and refined layering always comes down to fabric and fit.

The Secret to Layering Without Bulk

Bulk usually comes from heavy fabrics or poorly cut base garments. Here’s how to avoid it.

1. Choose Lightweight Thermal Underwear

For everyday Australian winters, you don’t need heavy alpine-grade thermal clothing. What works best is lightweight, breathable thermal undergarments that sit close to the body.

Modal blends are particularly effective because they offer softness, stretch and warmth without thickness.

A perfect example is the TBL Modal Cashmere Long Sleeve Top. It’s designed as a refined base layer top that fits smoothly under blazers, knits and structured jackets without creating bulk at the arms or waist.

For colder days, the TBL Modal Cashmere Long Sleeve Polo Neck Top provides additional coverage while still maintaining a sleek silhouette under coats and tailored outerwear.

The rule is simple: your thermal top should feel like a second skin, not an extra jumper.

2. Prioritise Stretch and Freedom of Movement

Layering should never feel restrictive. Whether you’re commuting, sitting at your desk or walking on the weekend, your base layers need to move with you.

Look for:

• Flat comfort seams
• Soft stretch fabrics
• A slim but not tight fit

The TBL Modal Cashmere Legging is a perfect example of a streamlined thermal bottom. It sits smoothly under trousers or denim, providing warmth without adding bulk around the thighs.

When base layer bottoms are lightweight and breathable, you’ll barely notice them, except when you step outside and feel the difference.

3. Think About Necklines and Sleeve Lengths

Layering well is also about being intentional with shape.

Under V-neck knits or blouses, a refined singlet base layer works beautifully. The TBL Cotton Singlet Top with Guipure Lace offers lightweight warmth while remaining discreet under clothing, making it ideal as a base garment beneath workwear.

For structured outfits, long sleeve base layer tops ensure warmth through the arms without the need for additional bulky layers.

The right neckline ensures your thermal underwear remains invisible while doing its job.

4. Choose the Right Thermal Bottom

Thermal bottoms, often referred to as long johns, should feel sleek, not padded.

A quality thermal bottom should:

• Sit flat under tailored trousers
• Provide warmth without overheating
• Maintain shape throughout the day

Lightweight modal and cotton blends are ideal for daily wear because they balance insulating properties with breathability.

Modal vs Merino Wool: What Works for Everyday Wear?

Merino Wool is well known for its insulating properties and natural bacteria resistance. It’s an excellent choice for outdoor activities or extreme cold conditions.

However, for everyday Australian winters commuting, office wear, travel and weekend layering, lightweight modal base layers often provide a more refined solution.

Modal offers:

• Luxurious softness against the skin
• Excellent stretch and freedom of movement
• Warmth without visible thickness
• A smooth finish under fitted clothing

If your goal is warmth without bulk, modal base layers are often the smarter choice for daily wear.

How to Layer Thermals Under Everyday Outfits

Let’s make this practical.

Workwear

Layer a long sleeve thermal top under:

• A silk blouse
• A tailored knit
• A structured blazer

Add a thermal bottom under tailored trousers for discreet warmth throughout the day. You’ll stay comfortable in air-conditioned offices without needing heavy outerwear indoors.

Weekend Casual

For brunch, errands or relaxed outings:

• Layer a thermal top under a soft jumper
• Add base layer bottoms under denim
• Pair with wool socks for added warmth

You’ll maintain a relaxed look while keeping body temperature steady.

Outdoor Activities

For walking, light sport or coastal mornings, breathable thermal underwear helps regulate temperature without trapping excess heat.

The key is temperature control, one quality base layer is usually enough.

Travel

Planes are notoriously cold. A slim thermal top layered under your outfit makes travel significantly more comfortable. Lightweight thermals also pack easily, making them ideal for winter trips.

Caring for Your Thermal Clothing

Quality thermal underwear should be practical to care for.

Most lightweight modal and cotton thermals are machine wash friendly. Always follow the garment’s care instructions to preserve softness, shape and heat retention over time.

Investing in well-made thermal undergarments means you’ll rely on them season after season.

Final Thoughts: Warmth Without the Bulk

Layering isn’t about adding more. It’s about choosing better.

When you invest in thoughtfully designed thermal underwear:

• You regulate body temperature naturally
• You reduce bulky outer layers
• You maintain a smooth silhouette
• You feel comfortable and confident all day

At The Foundation, we believe comfort is the foundation of confidence — especially in winter.

If you’re ready to refine your winter layering with lightweight, beautifully designed base layers, explore our collection.

Shop The baseLINE Collection

FAQs

1. Is thermal underwear only for extreme cold conditions?
   No. Lightweight thermal underwear is ideal for moderate Australian winters and everyday layering.
2. Will thermals make me look bigger?
   Not if you choose slim, lightweight base layers designed to sit close to the body.
3. Are Merino Wool thermals better than modal?
   Merino Wool is excellent for outdoor activities and colder climates, while modal is often better suited to smooth everyday layering.
4. Can I wear thermals under office clothing?
   Absolutely. A well-fitted thermal top and thermal bottom can be layered discreetly under professional outfits.
5. How many base layers should I wear?
   For most Australian winter days, one quality base layer (thermal top and/or bottom) is sufficient.