There are three elements required for a successful transfer: heat, pressure, and time (see Figure 6).
Figure : You need heat, pressure, and time

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Your iron must be as hot as possible. After you pre-heat your iron using the highest setting, do not reduce the temperature.
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You must press hard while you are ironing. To see how hard you need to press, place your bathroom scale on the ironing surface. Place both hands, one over the other, on the scale. Press down to generate 23 kilograms (50 pounds) of pressure. Use this same amount of pressure while you are ironing. Most people can achieve the required pressure by lowering the ironing surface and using their upper body for leverage.
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You must iron for the full recommended time. Make sure to iron the entire transfer evenly, paying special attention to the edges.
NOTE:
Important: If you do not use enough heat, pressure, and time, your transfer may crack or peel off the fabric.