I have found using scrap pieces of card can help. What I do is make sure the glue gun is nice and hot so the glue is very runny, spread a small amount on the edge I am currently working on and then using a scrap piece of card I spread the gluealong the edge I am glueing getting it thin and close to the edge. Then quickly press the other piece of foam to the glued area. Makes a nice even seam that is glued right to the edge. Wipe any and all glue that might ease through. What part of the Ironman helmet are you working on. I have completed several ironman helmets out of foam and might be able to help you out more.