Cotton, wool, cashmere and other sensitive fabrics are more likely to shrink as a result of hot water and heat. While the manufacturer's washing and drying instructions should always take priority, it is possible to make some adjustments in how you launder and dry your clothes to better promote shrinkage.
Test if the fabric is strong enough to stand up to high temperatures. Place the clothing in a sink of warm water. Add several cups of hot water to see if shrinkage occurs. Continue to add water until the clothing shows some shrinkage. Only use this method on clothes that can be laundered in warm to hot temperatures. Other clothing should be laundered as recommended by the manufacturer.
Launder the clothes at the same temperature at which the clothing started to shrink during the test (an approximation is sufficient). Use a washing machine, unless instructed otherwise by the manufacturer. Allow the clothing to cycle through completely. If washing by hand, allow the clothing to soak in hot water for several minutes after it has been laundered. Wait five to seven minutes before removing from the sink.
Remove the clothing from the washing machine or remove from the sink and wring it to remove excess water. The clothing should be damp.
Lay the clothing flat on a hard, flat surface. A table is ideal. Gently arrange shirts and pants so each corner is straight.
Turn the hairdryer to a high setting. Apply heat to each piece of clothing, section by section. Move from top to bottom or left to right as desired to heat the clothing evenly. Apply heat for two or three minutes.
Wring the clothing as tightly as possible, shaping each piece into a ball. Apply heat to each ball for two or three minutes, turning the ball and squeezing as you apply heat. Handle with care and do stretch the clothing at any time. The aim here is not to remove excess water, but to constrict the fabric and encourage it to shrink.
Lay the clothing flat on the hard, flat surface again. Apply heat for two or three minutes. Repeat the above steps until the clothing is completely dry. Iron to remove any wrinkles.