|You CAN preshrink the iron 0n interfacing so it won't ruin the garment by shrinking after its all sewn. Cut according to pattern, trim as described in the pattern directions, then lay it carefully in place. Hold a good steam iron about 6-10" above it and give it a heavy dose of steam. Very carefully, pick the interfacing up, then gently lay it back down. You will be able to see that it has shrunk some (how much depends on the kind and the size of the piece).