Ice Chest Backpack
It seems that when the family goes on a little jaunt that we always want something cold to drink. Or we want to take a picnic lunch and it would be good to keep it cool. We don’t want to lug around an ice chest so I decided to incorporate one into a back pack. I did this in a way that lets me remove the ice chest function so I can have a regular backpack or an Ice Chest Backpack.
The concept was to take some type of molded plastic container and then apply foam around it to provide insulation. I decided that a small (2 gal.) plastic trash can would work great and decided to use DIY spray foam as the insulation. I thought of using two part expanding urethane foam, but it is expensive and would be hard to source for some people so I decided on the "Great Stuff" spray foam.
I think it turned out quite useful.
Step 1: Materials
- 2 Gallon Plastic Trash Can (from Target)
. (You may want smaller or larger depending on your back pack size.)
- Can of “Great Stuff” Insulating Foam Sealant; Gaps and Cracks, 16 oz. (454g) - Home Depot
- 2 Pieces of HDPE (High Density Polyethylene) Foam 1” x 12” x 8-1/2”
. (I usually find this as packing material on high tech items)
- 30 inches of Hook and Loop Fastener; ¾” wide; Back to Back type - Dollar Tree
- Brown Paper Bag (Trash Can will fit into)
- Plastic Bag (Trash Can will fit into)
- Drop Cloth
- Packing or Masking Tape
- Nitrile or Latex Gloves
- Razor Knife
- Glue Gun and Glue Sticks
Step 2: Test Fit Your Trash Can Into the Brown and Plastic Bags and Backpack
You will be shooting the foam between the trash can and the paper bag. You can omit the paper bag if you want to make your backpack permanently a cooler. I decided that I wanted to be able to remove the cooler so I added the paper bag to contain the foam. I put the trash can and paper bag into a plastic bag so that if the paper bag failed during the foaming process I could still remove the cooler.
It should all fit nicely together with the bags going up above the lip of the trash can by at least an inch. There should be at least a half-inch between the trash can wall and the paper bag for foam. More is better :-).
Step 3: Add a Foam Collar to the Trash Can - Trace the Can
In this step we are going to create a 'donut' (collar) that the trash can slips into. The collar slides up under the lip of the trash can.
Three reasons I added a foam collar to the trash can:
1. I wanted to dress up the trash can a bit - so it looked like a bit more than just a trash can.
2. I wanted to have a vertical surface to have the paper bag snug up against / around.
3. I wanted to make sure I didn't have the edge of a hard plastic trash can digging into my shoulders :-).
You need to take the HDPE foam and trace the largest outline of the trash can flange/perimeter at the opening. Then draw a ring inside that flange tracing to match the actual opening of the trash can. Then you need to trace a line larger than the flange - This is the width of the collar that extends out larger than the perimeter of the trash can.
From outter to inner:
A. Edge of collar
B. Traced trash can perimeter
C. Opening for trash can to slip into. (The piece removed to make this opening will be used for part of the lid.)
A and C are cut and based on B - the tracing of the trash can.
Step 4: Cut Out the Collar
Carefully cut out the collar center hole and slip the trash can into it. You want to only cut where needed - don't make any other holes in the center of the piece you are cutting out as this will end up being the part of the lid that fits down into the cooler (trash can) opening.
You can then cut the perimeter of the collar. For some of the cutting I followed my traced outline, for others I looked at the trash can and freehanded it around the lip.
Your razor knife may have a long enough blade, you may have to make two passes or you might want to get one of the cheapy snap-off segmented razor knifes at the dollar store so you can have a really long blade.
Step 5: Glue the Collar to the Trash Can
Hot glue the collar to the trash can so it's firmly attached. I had a bit of a larger gap than I wanted between the HDPE foam and the body of the trash can so I just filled the gap up with hot glue.
Be careful on the temperature of your hot glue as high temp type may melt the HDPE foam. I had to drop the setting down to the low temp setting.
Step 6: Hot Glue the Lid Straps
I decided that I would have a simple press-fit lid that I wanted to make sure stayed in place so I cut my 30 inches of hook and loop fastener (hook on one side, loop on the other) in half to make two 15 inch pieces.
I hot glued them to the side of the trash can. Make sure they overlap sufficiently and also that they are oriented so that they grab. Note: I purchased my hook and loop from the dollar store and it came as two 30-inch pieces; one of self-adhesive hook and another of self-adhesive loop. I stuck them to each other and it made my back to back closure strap (last photo in this step.)
Step 7: Cover the Lip of the Trash Can and Collar
I figured that spray foam would end up getting everywhere and I wanted to make sure that my cooler looked nice so I masked off the HDPE foam and trash can lip with packing tape so that any foam that sneaked out wouldn't stick and be an eyesore. I also stuffed the trash can with some extra plastic grocery bags to prevent foam from landing in the inside of the trash can. Cover the hook and loop lid strap also.
Step 8: Fit It All Together in the Backpack - Mark Depth
Now fit all the components together as it will be when foamed. Push the trash can down so it bottoms out in the backpack. then pull it up about an inch (the desired thickness of the foam on the bottom) and make a mark on the inside of the paper bag. This line indicates the level you want to pull up the trash can after you apply foam so that you have 1" of foam on the bottom.
Step 9: Start Foaming
Put on your gloves -- this foam is sticky and permanent. Make sure you have a drop cloth down and are wearing clothes that you don't care if you ruin them.
Follow the spray foam manufacturer's instructions. Foam and foam propellant are flammable so keep away from sources of ignition and use with adequate ventilation.
You want to pull the trash can out of the paper bag and then shoot a bunch of spray foam into the bottom of the bag to about an inch depth. Cover the bottom well, then quickly insert the trash can back into place. Pull the trash can up to the depth mark you make in the last step. Make sure everything is lined up so the trash can is parallel to the shoulder straps, etc.
Now start sticking the applicator tube of the spray foam down the sides of the paper bag between the paper bag and the foam collar and inject foam. Move around the collar and try to get the foam evenly distributed. I used an entire 16 oz. (454g) can.
Step 10: Remove Cooler Assembly and Mist Paper Bag
The spray foam stops being tacky at about 15 minutes. I let it harden for about 30 minutes before removing the cooler assembly from the backpack. You want to remove the plastic bag so the foam can cure faster. If the paper bag tore you will have to leave the plastic bag in place until the foam is completely cured. The info on the can of foam says 8 hours for a full cure, but since this is a much thicker application I would think it would be wise to wait at least 24 hrs.
The can instructions state, "Mist water to speed cure" so I used a hand spray bottle to lightly dampen the paper bag before putting it back into the backpack. It's important to keep the cooler assembly in the backpack until the foam is completely cured and has stopped expanding. If you prematurely remove the cooler assembly it might expand slightly and not fit back into the backpack.
Step 11: Clean Up Stray Foam and Trim Paper Bag
Remove the packing/masking tape from the trash can lip and foam collar. Trim the paper bag so it is flush with the top edge of the foam collar.
Step 12: Cut the Lid Foam to Size
Take the piece of HDPE foam that you cut out to allow the trash can to slide into the foam collar (center of the foam collar that was removed) and trim it ever so slightly so that it press-fits nicely into the opening of the trash can.
Now take a new piece of HDPE foam and use the center of the foam collar that you just trimmed (to fit into the trash can) and use it as a template to cut a larger piece that approximates the size of the foam collar. This will be the flange on the foam lid.
Step 13: Glue the 2 Pieces of HDPE Foam Together to Make the Cooler Lid
Hot glue (being careful to use the cool setting) the two pieces of HDPE foam together to make the cooler lid.
The lid snuggly fits into the opening of the trash can and is held in place by the hook and loop fastener tape.
Step 14: Now Enjoy Your Backpack Cooler - Go Take a Hike!
I would keep the cooler in the backpack for several days to allow the spray foam to fully cure and stop expanding.
Now load up with some ice and drinks, and whatever else needs to be cool, and ENJOY!