Step 1: Materials
I used foam sheets from Michaels. The larger costume for my 6 year old to 9 of the 12" x 18" sheets. He's 50" tall and weighs 50 lbs. I used a combination of a glue called Quick Grip (which held very well and stayed flexible but is messy and needs to dry overnight) and hot glue (for adding some of the detail work.) By the time I got to my daughter's costume I got a little impatient and used the hot glue for most of the glueing. I worked ok as long as you are quick with getting the pieces together quickly. But it does deform the foam a little and it is not flexible. You're also gonna need a couple of packages of white velcro strips (18" in length). And you'll need a length of 1" wide black elastic for the upper arm pieces - both for a strap around the arm and to attach them to the shoulder straps. I also used some to hold the thigh pieces up - one end hot glued to the thigh piece and the other has a velcro piece that attaches behind the belt.
Step 2: Paper Templates
The first step was to make paper templates for each of the armor pieces. This allows you to size them by fitting them temporarily with tape and then shaping them with scissor around joints and what not. I used 8.5" x 11" paper - taping two pieces together for the larger templates.
Step 3: Helmet Construction
This was the most difficult part to create. I purchased the three quarter mask from Amazon and then found a generic astronaut helmet on a different site. both were under $10 each. I cut the top of the mask and removed the visor and cut the chin piece off of the helmet. The black brow on the mask lines up with the top edge of the helmet. I then attached the mask with two rivets through the ear pieces. The to get a full ear piece and a more finished look I cut of the bottom of two small Glad Ziplock containers and affixed them with a small bolt and nut. I then got some flat white spray paint and repainted the helmet so all the pieces match. Be sure to remove the stickers so you can replace them later.
Step 4: Applying Templates to Foam
The bulk of the work obviously is taking the paper templates and using them to cut the foam. It's important to get as many pieces out of each foam sheet and to save all the scraps for the smaller detail pieces. Use brand new xacto blades and change them often. When glueing the trim and other pieces be sure to apply pressure over night under some heavy books to get the smoothest surfaces and the strongest hold. Use velcro for closures but be aware that while initially the adhesive on the velcro seems strong enough after a few times of putting on and taking off the costume the velcro strips will let go from the foam so I suggest using hot glue instead of relying on the adhesive. The gloves are just cheap knitted gloves and the foam pieces hot glue easily to them. You'll use the elastic on the upper arm pieces to both strap around the arm and to attach them to the shoulder straps. Also use some for supports on the thigh pieces, attaching a piece of velcro to the loose end to attach to the inside of the belt.
Step 5: The Competed Costume
To complete the costumes we used black thermal underwear for the jumpsuit. Hope you guys like the result. Have fun.