Suits are made in a variety of fabrics, but most commonly from wool. The two main yarns produce worsteds (where the fibres are combed before spinning to produce a smooth, hard wearing cloth) and woollens (where they are not combed, thus remaining comparatively fluffy in texture). These can be woven in a number of ways producing flannel, tweed, gabardine, and fresco among others. These fabrics all have different weights and feels, and some fabrics have an S (or Super S) number describing the fineness of the fibres measured by average fibre diameter, e. g. , Super 120; however, the finer the fabric, the more delicate and thus less likely to be long-wearing it will be. Although wool has traditionally been associated with warm, bulky clothing meant for warding off cold weather, advances in making finer and finer fibre have made wool suits acceptable for warmer weather, as fabrics have accordingly become lighter and more supple. Wool fabric is denominated by the weight of a one-square yard piece; thus, the heavier wools, suitable for winter only, are 12–14 oz. ; the medium, “three season” (i. e. , excluding summer) are 10–11 oz. ; and summer wools are 7–8 oz. (In the days before central heating, heavier wools such as 16 oz. were used in suits; now they are used mainly in overcoats and topcoats. ) Other materials are used sometimes, either alone or blended with wool, such as cashmere. Silk alone or blended with wool is sometimes used. Synthetic materials, while cheaper, e. g. , polyester, are very rarely recommended by experts. At most, a blend of predominantly wool may be acceptable to obtain the main benefit of synthetics, namely resistance to wrinkling, particularly in garments used for travel; however, any synthetic, blended or otherwise, will always be warmer and clammier than wool alone.  For hot weather, linen is also used, and in (Southern) North America cotton seersucker is worn.