What Are the Benefits of Thermo Aspen? 5 Reasons It Works in a Sauna

It remains comfortable to touch at all times

This is the benefit you notice first. Aspen is a light, low-density timber, and its cells hold a lot of air. Air is a poor conductor of heat, so the surface of the board feels warm rather than hot, even when the air in the room is far hotter than you could comfortably touch on most other materials.

That matters most on the benches, where bare skin sits directly on the timber for 10 or 15 minutes at a time. A dense hardwood bench can become uncomfortable to sit on once the stove has been running for a while. Thermo Aspen stays comfortable, so you can lean back and relax instead of perching on a towel.

Great stability and a long lifespan

A sauna puts timber through a tough routine: it heats up, gets steamed, cools down and dries out, often every day. Ordinary timber swells and shrinks with each cycle, which is how boards cup, joints open up and fixings work loose.

Thermo Aspen moves far less than ordinary timber through that routine. Day to day, that shows up in three ways: boards stay flat instead of cupping, the joints between them stay tight instead of opening into gaps, and the fixings stay put instead of being worked loose. It is also much better at resisting rot than untreated timber. If you want to know how the treatment itself works, our guide to the thermal modification process explains it step by step.

Lifespan comes down to how the sauna is looked after as much as the timber itself. Leave the door open after each session so the room dries out, and keep the ventilation clear, and a Thermo Aspen lining is built to last for many years.

A smooth machined finish

Our Thermo Aspen arrives planed smooth and precisely profiled, so it is ready to fit straight from the pack. The channel groove cladding locks together neatly for walls and ceilings, leaving a clean, even shadow line between boards. The PAR + Rounds bench slats have their edges rounded off, so there are no sharp corners against the back of your legs.

A smooth surface is also a practical one. There is far less sanding to do on site, the boards resist splintering, and a smooth face is easier to wipe down and keep clean between uses.

A superior quality grade

Sauna timber is selected to a higher standard than general-purpose cladding, and Thermo Aspen is no exception. The boards are straight-grained and low in knots, and thermal modification gives them a warm, honey-brown colour that runs right through the timber rather than sitting on the surface.

In practice, that means a sauna that looks consistent from wall-to-wall creating a high-quality sauna finish, less time picking through boards to avoid defects, and less waste. Fewer knots also means fewer weak spots and nothing to weep or loosen with heat. Our Thermo Aspen is also FSC®-certified, so you know it comes from responsibly managed forests.

In stock and ready to go

A lot of sauna timber sold in the UK is imported to order, which can mean waiting weeks before a project can start. We hold our Thermo Aspen cladding and bench slats in stock at our yard in Moreton, Essex, with UK delivery or click and collect available.

If you would like to see and feel the finish before you commit, you can order a sample first. When you’re ready, browse the full range of Thermo Aspen sauna cladding and bench slats.

Planning your sauna build?

Our UK buyer's guide to the best wood for a sauna covers the practical side of a build: Thermo Aspen vs standard Aspen, the difference between cladding and bench slats, how much timber you need, fixings, and what to use on the outside of a garden sauna.

FAQ’s

Does Thermo Aspen have knots?

Very few. Thermo Aspen for saunas is selected for straight grain and a low knot count, so walls look even and there are fewer weak spots in the boards. As a natural timber, you may still see the odd small, sound knot, but nothing like the knotty pine panelling sold for general interiors.

Does Thermo Aspen smell?

Freshly machined Thermo Aspen has a mild, slightly toasted scent from the thermal modification process. It is subtle and tends to soften over time. Unlike resinous timbers, it does not give off sap or strong oils when heated.

Does Thermo Aspen splinter?

Thermo Aspen is smooth-faced and resists splintering, which is one of the reasons it is used for sauna benches. Our bench slats also have rounded edges, so there are no sharp corners where you sit or lean.

Need help with your project? Contact our team here or call us on 01277 890783 and we will help you choose the right profiles and lengths for your sauna.