Wool versus plastic filling: what your dog is actually sleeping on

The three fillings

Polyester fibrefill is spun plastic staple, cheap and light, which loses loft as the crimp collapses under repeated compression. Polyurethane memory foam is a chemical foam that softens with body heat and holds a shape. Wool is a hollow, crimped protein fibre, either loose as a filling or wet-felted into a single dense structure.

Moisture is the whole story

A sleeping dog gives off heat and moisture all night through its paw pads and its breath. Polyester and foam are hydrophobic: the moisture does not go into the fibre, it condenses at the surface and sits there. That damp film is what feeds the bacteria that produce the sour smell every foam bed eventually develops, and it is why anti-microbial finishes exist at all.

Wool absorbs up to around thirty per cent of its own weight in moisture vapour into the fibre itself while still feeling dry to the touch, then releases it back into the air during the day. The bed dries between uses instead of accumulating.

Temperature works in both directions

Memory foam is an insulator that stores body heat and returns it, which is comfortable for an arthritic dog in February and miserable for a thick-coated dog in July. Wool's crimp traps still air in winter and its moisture handling gives evaporative cooling in summer, so the same bed works in both seasons. This matters most for double-coated breeds and for cats, who will simply abandon a bed that runs hot.

Dust mites, allergies and off-gassing

Dust mites need humidity to survive; wool's moisture regulation and lanolin make it a poor host, which is why wool bedding is a standard recommendation for allergic households. Foam beds hold humidity in the cover and typically off-gas volatile organic compounds for weeks after unwrapping — the new-bed smell — and are often supplied with a flame retardant that wool does not need, because wool is naturally flame-resistant.

Lifespan and price per year

A fibrefill bed goes flat in six to twelve months of nightly use. A mid-range memory foam bed compresses and yellows over two to three years, and cannot be repaired because a torn foam core is finished. A felted wool bed densifies rather than collapses — it gets firmer and better-shaped for the first year and can be re-felted, patched or re-covered.

Priced across a decade rather than a checkout, wool is usually the cheaper option, and it is compostable at the end rather than landfill.

When foam is genuinely the right answer

We will say it plainly: a large senior dog with hip dysplasia or advanced arthritis needs measured pressure relief, and a good orthopaedic foam core delivers that better than felted wool. The sensible compromise is a supportive core in a wool-and-cotton cover, so the surface the dog breathes into is still a natural fibre. Anything with heavy incontinence also argues for a washable waterproof layer, though wool copes with far more than people expect.