The use of fabric is so variable that it's difficult to give hard fast advice on how it might behave in different situations. For example velvet can change its finished length by the fibers relaxing in certain atmosphere. The longer and heavier the fabric is the greater the finished length may alter over a period of a few weeks. Viscose and rayon may shrink or relax in different humidity. Cotton velvets may drop considerably as may looser weave fabrics. For this reason curtains should be made with a good-sized hem, loosely sewn as with side seams. Any linings should also be slip stitched. This will allow for any possible movement when the curtains are hung. Alternatively, lengths can be cut and hung over a banister where the atmospheric conditions are the same as to where the curtains are going to be hung.
Fading
All fabrics will eventually fade but dark dye silks will fade particularly if they are in direct sunlight. Avoid dark colors at very sunny windows where possible and always use a good solprufe lining to protect fabrics. Keep furniture, where upholstery fabrics have been used, out of the sun.
Shrinkage
All fabrics are susceptible to shrinkage particularly natural fabrics such as cotton and linen. You should allow up to 6% shrinkage when making curtains and loose covers. Fabrics may also shrink with dry cleaning. When making loose covers it is important to allow for shrinkage. Tight fitting covers look the best but be aware that, after washing, the loose covers will shrink. The initial fit should allow for up to 6% shrinkage.
Please note that any accessories or trimmings used on cushions etc may shrink at a different rate. Also it is important to use the correct cotton for sewing as this can shrink at a different rate and spoil the look of curtains or cushions etc.
Cleaning
Most fabric companies suggest dry cleaning and it is important to follow the recommendations for care otherwise problems can not be put right at a later date. Most loose covers are better dry cleaned as there is less room for shrinkage and they come back pressed and generally look better. However, some people prefer washing cushions etc particularly where there are young families. This is possible with natural fabrics but its best to test a sample piece first to check how the fabric might react.
Pattern Repeats
If there is a pattern repeat to the fabric you choose always make sure before you cut into it that the patterns are aligned for curtain use. The majority of pattern repeats adhere to the specifications given in the pattern book but occasionally a variance might occur, particularly with woven fabrics. No company will accept responsibility for this once the fabrics have been cut into so it is very important to check first that you are happy with how the widths of fabric join up.
Fabric suitability
Check with your supplier first that the fabric you have chosen is the correct fabric for the job you require it to do. Fabrics used for covering furniture are usually given a rub test and then categorised in to Careful Domestic, General Domestic, Severe Domestic or general contract or Severe Contract. A family with children climbing on and off the sofa is going to require a general domestic fabric whereas a sofa used occasionally may be OK with careful domestic.