The Flat Head - Heavyweight Thermal Long Sleeve Black [FN-HTHL-001]

The Flat Head FN-HTHL-001 Heavyweight Thermal takes a traditional cold-weather base layer and builds it with the substantial fabric and meticulous construction the brand is known for. Knitted from thick No. 10 single cotton yarn, it has considerably more weight and texture than a conventional thermal while retaining the stretch and comfort that makes this style so useful through the colder months.

The fabric uses an elongated honeycomb structure with pronounced peaks and valleys running across the surface. Those deeper pockets hold more air than a flatter knit, improving insulation without relying on synthetic fibres or excessive bulk. The structure also provides excellent horizontal stretch, allowing the shirt to sit relatively close to the body while remaining comfortable in motion.

Because The Flat Head uses such a thick cotton yarn, the honeycomb texture is considerably more pronounced than on a standard thermal. The result is a dense fabric with enough substance to work beneath denim and leather jackets as a proper insulating layer, but enough body to wear on its own almost like a lightweight cotton sweater.

The construction receives just as much attention as the fabric. The main seams are sewn using four-needle flat-seam construction on a vintage Union Special flatseamer dating from the 1960s. Rather than stacking fabric and creating a raised seam against the body, the flatlock construction keeps the inside surface smooth, making the thermal considerably more comfortable when worn directly against the skin.

Both shoulders are reinforced with additional rib-knit panels. This protects the stitching from repeated friction, particularly when another garment is worn over top, helping prevent premature thread wear. The neckline uses The Flat Head’s familiar three-needle construction with one needle offset from the others, sewn with heavy No. 20 cotton thread to help the collar retain its shape through repeated wear and washing.

Finished in Black and one washed, the FN-HTHL-001 is a simple piece on the surface but one where the difference is almost entirely in the fabric and construction. The dense honeycomb knit provides warmth, stretch and texture, while the vintage flat-seam sewing makes it comfortable enough to wear directly against the body throughout the colder months.

Made in Japan.

Key Features

• 100% cotton

• Heavyweight Japanese thermal fabric

• Thick No. 10 single cotton yarn

• Elongated honeycomb knit structure

• Pronounced raised surface texture

• Excellent horizontal stretch

• Close, comfortable fit

• Honeycomb structure traps air for added insulation

• Dense enough to wear as a base layer or on its own

• Reinforced rib-knit shoulder panels

• Four-needle flat-seam construction

• Sewn using a vintage 1960s Union Special flatseamer

• Flat interior seams for improved comfort

• Signature three-needle neckline construction

• One needle offset at neckline

• Heavy No. 20 cotton thread

• One-wash finish

• Black colourway

• Made in Japan

• Style FN-HTHL-001

• Also available in Ivory
  
• Shop more styles from The Flat Head

Fabric & Care

100% cotton heavyweight honeycomb thermal.

The Flat Head uses thick No. 10 single yarn to create a deep honeycomb structure with considerably more surface variation than a standard thermal knit. The raised construction traps air between the body and fabric, improving insulation while allowing the cotton to remain breathable.

The fabric has substantial horizontal stretch and is designed to sit relatively close to the body without restricting movement.

The garment has received a one-wash treatment, so the majority of the initial shrinkage has already occurred. Some additional settling may still happen depending on washing temperature and drying method.

Wash cold with similar dark colours and hang dry. Avoid excessive heat to help preserve the fit and honeycomb structure.

Fit

Trim, close-fitting Japanese thermal silhouette with significant stretch through the body.

The FN-HTHL-001 is designed to work comfortably as a base layer, so the chest measurements can appear quite narrow when laid flat. The honeycomb knit stretches considerably across the body once worn.

The Flat Head sizing runs relatively small compared with typical North American sizing. Customers wanting a close base-layer fit can stay closer to their usual Japanese size, while those looking to wear it more like a standalone sweater may prefer to size up.

We recommend paying particular attention to the shoulder and length measurements when choosing your size, as the body itself has considerably more stretch.

Garment measurements taken flat before wash. Compare against a piece you already own and love.

How we measure

Canada: free Standard shipping over $300 CAD, otherwise $19.99 in BC and $24.99 to the rest of Canada. Express is $33 flat. Tracked courier, 1 to 4 business days.

United States: free Standard shipping over $350 USD, otherwise $25.99 USD. Express is $30 USD.

Returns: read our Return Policy for full details on returns and exchanges.