What goes beneath a rug: the underlay

One unrolls a rug on a waxed parquet, takes a step, and it slides away with the foot. What slips beneath it to prevent this is called an underlay, known in French as a thibaude or sous-tapis. It is a layer of felt, rubber, jute or synthetic foam placed between the floor and the rug. Thibaude is the term preferred by terminologists; sous-tapis is used in everyday French. It has three effects: it holds the rug in place, it cushions the step, and it reduces the friction of the rug against a hard floor, which helps it better resist wear. The Office québécois de la langue française distinguishes two forms: the attached underlay, bonded to the rug, and the loose underlay, laid separately. Beneath a hand-knotted or hand-tufted rug, it is the loose underlay that serves, chosen according to the floor, the room and the technique of the rug.

What is an underlay for?

It serves first for safety. On tiles, polished concrete or a varnished parquet, a rug laid bare can slip at the first hurried step. A non-slip underlay holds it, including in a passage or at the foot of a staircase.

It serves next the rug itself. The lexicon of Centexbel, the Belgian technical centre for textiles, defines it as a layer that reduces the friction of the covering against a hard floor, with the effect of better resistance to wear and greater walking comfort. A rug that stays in place rubs less against the floor, and it keeps its shape better underfoot.

Felt, rubber, foam: which material?

The reference definitions cite the same families: hair and jute, felt, sponge rubber, urethane and polyurethane foams. Rubber works mainly on grip; felt and foams work on cushioning.

The choice is made from the floor. A hard, smooth floor calls first for grip. A rug laid on carpet, or a rug one wants softer underfoot, calls rather for cushioning. Thickness also matters for doors that must pass over it.

Knotted or tufted, the technique changes the question

Our rugs hand-knotted in Nepal are supple: they fold, which incidentally eases their transport. Our rugs hand-tufted in India are stiffer and do not fold. The technique of the rug therefore enters into the choice of underlay, just as the floor does. Hand-knotting is also more rustic to the touch, hand-tufting more even. The two crafts are presented on the pages the hand-knotted rug in Nepal and the hand-tufted rug in India.

On a heated floor, every layer counts

On underfloor heating, the underlay adds to the thickness of the rug and also slows the heat. The British maker Cormar, drawing on research by the UK underfloor heating manufacturers' association, recommends for carpet that the combined value of the covering and its underlay remain below 2.5 tog, the unit of thermal resistance used across the Channel. The question is treated in detail in our article on the wool rug and underfloor heating.

A well-chosen underlay is part of caring for a rug: it holds it, and it wears less. The other gestures, from vacuuming to stains, are gathered in our guide to caring for a wool rug. For a specific room, the best course remains to bring the dimensions and the nature of the floor to one of our Paris showrooms.

Text written by the house of Diacasan Edition, Parisian publisher of artists' rugs, from the terminological definitions and technical sources cited below, and from interviews with its founder on our techniques, October 2026.

Sources: Office québécois de la langue française, Grand dictionnaire terminologique, fiche thibaude; Centexbel, lexicon, Carpet underlay; Cormar Carpets, Tog values.