I've finished my costume and I hit London Comic con back in October.
The costume got a lot of attention, seriously, got stopped every 10 seconds for a picture of my Soundwave costume.

It took a little damage though, what with moving around an all. I manage to fix most of it but I've come across one problem I need some advice on.

My boots.

I found out there's a little extra space in the boots and want it a little more snug around the leg, is there anything I can use to fill the gaps?

http://www.facebook.com/media/set/?set=a.1...=3&l=a5d92cf7fa

I'd say just layer sheets of foam on the inside. If this thing is going to have direct contact with your leg and you want it snug, I'd go with the foam.

Agreed. Light foam's a good choice. You can even wrap a sheet around your leg and slit it where the corners of the costume leg will slip over it, to give it a squarer shape. Or cut strips of foam with triangular cross-sections and wedge them inside the long edges of the costume so that the interior is more of an octagonal shape.

If the foam turns out to be too heavy or too heat-retentive, just use thin spirals of foam at both ends of the legs so that they grip your own legs in two places instead of all along it.