Yip Yip Costume




Whether you loved them as a kid or hated them for giving you nightmares, there's no denying it's fun to go around freely and anonymously shouting "yipyipyipyip" to those around you. Here's how to make a costume based off the Martian Yip Yip aliens from Sesame Street.

UPDATE: Some pics from WonderCon 09!


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Step 1: Materials

5-6 yds of Curly Fleece
I've found this fabric to work well for the body of the costume. It's soft, breathable, and light enough to move around in but with enough weight to hold the package together. The downside to curly fleece is it can shed quite a bit when it's fresh, so it gets rather messy. However, a good thing about this is that the fur on the fabric was so long that it easily hid the many safety pins I used. Another good option is something called Flurr (fleece + fur). You want about about 2.5-3x whatever your height is.

1-1.5 yds of Black Chiffon/Mesh
This is the mesh-like material that will form the mouth. It is important that the material be see-through, since this will be your window to the outside world. The mouth will probably consist of 2-6 layers of this material, depending on the specific fabric you have. The most important part is that if you hold it up to your face, you can see relatively clearly through to the other side (usually there is a light source outside of your costume), but no one can see into your costume through the mouth (no light source within your costume).

Contour Shaped Sponge
You can pick this up at your local Home Depot for a few dollars. A good half-oval shape is what you want. The dimensions I found were 7.5"x3.5"x2.5", and I eventually cut in half length-wise however. This will form the lip.

Styrofoam Spheres (x2)
For the eyeballs. 4" in diameter will do, or 5" if you want to go bigger.

This will be essential to keeping the costume on your head. Pick out something that is light, nothing too thick. You don't want to start sweating too much while wearing the costume. It should have enough structure to it though stay firm and not flop around.

Pipe Cleaners
This should match the color of your costume. Thin pipe cleaners work well, you just need to buy enough of them to twist around to make a solid and flexible pair of antenna. Some glittery pipe-cleaner is also helpful in complimenting the solid colors.

Other materials:
Hot glue gun
Needle and thread (or staples)
Safety pins (various sizes)
A friend (very helpful to have someone to wear the costume as it is being created)

Step 2: Measuring the Mouth, Part 1

Drape the body fabric over your head length-wise so it runs from your heels, over your head, and down to your toes. However, give yourself approx 1 1/2-2' of extra length for the front half. This is because you'll need the slack for when you lift up what will be the jaw portion of the costume to move the mouth. Duct tape is a handy measuring marker for this step. While draped in the fabric, mark these points on the fabric:

Center of the top of your head
Eyebrow line (approx upper edge of mouth)
1 3/4' from the brow line to the lower edge (of the mouth)

These will be markers for cutting out the mouth hole. The dimensions of the mouth hole are approximately 1' in width, and 1 3/4' in length, oval shaped. Mark the left and right edges of the mouth hole as well. Your eyebrow line will be the the approximate upper edge of the mouth. Be sure these markers all line up symmetrically with the length-wise axis of the fabric.

Next, cut out the mouth hole. Better to under-estimate here, you can always increase the size of the hole with more cutting. Keep in mind that whatever you imagine the hole size to be, leave a small 1" buffer between the edge of your cut, and the true edge of the mouth. This is because you'll need that flap to sow on the mouth covering.

Post Note: I recommend making the upper area of the mouth slightly more square than rounded. This is so that you will have enough room to have a bit of peripheral vision when you look through. If you don't manage this, you can widen the width of the hole by fastening the fabric to your beanie accordingly.

Step 3: Measuring the Mouth, Part 2

Next cut out a rectangular piece from the black mesh to act as the mouth fabric. Be sure it has plenty of space to cover the hole. Depending on the transparency of your fabric, you'll need several sheets to form the mouth. With my fabric, 3-4 layers was enough.

A good test of the visibility is to hold the total number of sheets close to your face and use a take a picture of yourself (with flash on) from several feet away. Your silhouette should not be visible, or only very slightly. At the same time, you should be able to see through the fabric and walk around a dimly lit room at least.

Step 4: Sewing the Mouth

Here comes the tough part. After you've decided how many layers you want to form the mouth, you're going to sew them to the body fabric to cover the hole. It helps to tape the black sheets together first so they can be sewn on all at once. This part can get frustrating as each layer may move about on it's own, but just take your time. The good thing is, complete accuracy isn't important, from the outside, no one can tell.

IMPORTANT: Be sure you're sewing the mouth fabric to the inside of the body, not the outside.

If you're not comfortable with a needle and thread, ask a friend who knows how to help you. Stapling is also an option, but that depends on the thickness of your mesh mouth fabric. After you've sewn the mouth fabric on to the body fabric, you can trim the loose flaps to clean up the area. From the outside it should look like a nice gaping black hole.

Note: A commenter suggested using hot glue for this step, which probably would make things alot easier.Other commenters have used velcro strips to make the mouth area detachable. This sounds like it would be especially helpful if you want to be able to show your face easily without taking off the whole costume.

Step 5: Fitting the Beanie

You've probably noticed by now that when draping the body over yourself, it tends to slide around a bit. To fix this, you'll need to attach your beanie to the inside, right where you've marked the center of the top of your head. You can use large safety pins to get a rough position, then lock it down in place with smaller ones around the rim. When adjusting the placement, be sure your eyes are just beneath the upper edge of the mouth fabric, so you can see out through the mouth. However, you don't want your eyes to be too low into the mouth, or it may look like either your Yip-Yip is always looking down, or it's upper lip is wrapping around your forehead.

Step 6: Creating the Jaw

With the dimensions of the sponge I bought, I cut it in half length-wise to make it thinner (easier to handle). Mark an area a few inches past the lower edge of the mouth, and tape the curved face of the sponge onto the inside surface at that location. This is where all the movement will take place. Try moving the jaw up and down while looking in a mirror, to make sure it looks ok. When you're satisfied with the placement, hot-glue the sponge on.

Once the jaw is attached, you may notice the mouth fabric feeling a bit floaty. You can weigh it down to give a it a better sense of being a "mouth" by pinning a small weight to the inside of it to create a sort of "throat". A knot of left-over fabric works well for this.

One tip, when holding up the jaw in the "closed" state, your eyes should fit just between the tip of your jaw and the upper edge of the mouth. This way you can still see without your Yip Yip opening his mouth.

Step 7: Creating the Eyes

While inside the costume, have someone else mark a good position for the eyes, just based on whatever looks best. Another option is to lay the costume out flat on the floor, then lay the eyes on the approximate area according to what appears symmetric. Once you have that, you can hot-glue the balls directly onto the fabric. I prefer to have the eyes touching each other, so I glue them together as well.

Test the eye position by placing the costume on with the beanie a comfortable and even place, then look if the eyes appear to be straight and level. When that is taken care of, cut out a pair of circles for the pupils out of black paper (mine were about 1" in diameter), and glue them onto the Styrofoam balls.

Step 8: Creating the Antenna

Take the pipe cleaners and wind them up into a single shape as seen in the images. I used about 24 total pipe cleaners to get the structure right, with more making up the base and less around the ends. When it was all wired together I lined it with four glitter pipe cleaners, just because.

When you have the finished antenna, affix it to the head area with safety pins, just behind the eyes. The safety pins can go through the beanie for extra support. Adjust the antenna so it stands up straight when the costume is worn normally.

Step 9: Finishing Touches

While inside the costume, have someone start sealing up the sides with safety pins. Fold the flaps inward and close them up. The safety pins can be about 6-8" apart, going down the side. Just clean it up however you feel comfortable, as long as you can keep others from seeing into the costume from the sides. Don't close it up too tightly though, you need space to move around, and to maintain the Yip Yip look. It doesn't have to be super neat, the Yip-Yips have a pretty sloppy look. And in the end, you're still essentially just wearing a sheet over your head. (Commenters have opted to sew up the sides or use velcro strips, both which work fine. Safety pins are probably the fastest option. In any case, you may want to leave a hole for you to let your arms stick out in case you'll need them)

With the sides sealed up, you can get to work on the front and back edges. What I did here was cut vertical strips up length-wise like a flier with tear-away phone numbers. I also cut out strips from left-over fabric and attached it to the ends. The more the better, it will help to cover up your feet and legs. Not too long though, you don't want to trip over it. The idea is just to give the costume that ghosty-alien look. You can either hot-glue the extra strips on, or use safety pins, whichever you prefer.

That just about wraps it up. If you need to adjust how the costume fits, you should be pretty comfortable by now with how much flexibility you have; I used safety pins pretty liberally as they aren't easily seen anyways being fastened on the inside. When not wearing the costume it seems easiest to handle it with your hand inside the beanie like a puppet; this way none of the headgear flops around too much. Feel free to give me feedback, or share any ideas you've added to your costume.

yipyipyipyipyipyipyip...uh huhh, uh huhh

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156 Discussions


Tip 5 weeks ago

After watching many videos explaining who the yip yips were, I finally talked my tween/teen boys into these costumes. They were a HUGE hit! I could only find one color for the curly fleece so I used the no pill fleece from JoAnns, safety pins, hot glue, duct tape, and velcro. I used the safety pins to attach the sides, leaving a space for their arms to come out. Hot glueing straight onto the fleece is 1 1/2 " pipe insulation foam...we broke up a wire hanger to add inside the foam to help keep the shape of the mouth. Used the "hook" from the hanger on the bottom lip to move the yip yips mouths a little easier. Duct taped the ends of the foam to keep the wire in. We only used one piece of the black mesh. I hot glued up the sides of the mouth and used velcro on the top and bottom...top so they could show their faces w/o removing the whole costume, and the bottom for the candy...they were holding bags inside of the costume. I cut the pupils out of felt and hot glued them onto the 4" styrofoam balls...let the hot glue cool for a couple of seconds before adding to the styrofoam, so it doesn't melt. Hot glued the eyes and antenna's straight to the fleece. Then I hot glued some more after the first round had dried. My cost was roughly $42.00 per costume. Had it not been a last minute costume, I would've bought the fleece one color at a time with a coupon. Few things to pass on...wearing the fleece is HOTHOTHOT...basically, they were wearing a blanket. Luckily, Colorado has been super cold this year so it worked out. I like to think I'm pretty crafty but this is definitely not a project for one set of hands...have a helper! THANK YOU!THANK YOU!!THANK YOU!!! for the idea and the instructions!!!


14 years ago my Husband, his brother and I made the Yip Yip's {pictured with their Mom}. 2017 we brought them out for the Pumpkin Village. Still a "HIT" after 14 years..

Yipyips.jpgyip yip 2.jpg

1 year ago on Step 9

Just made this for an office party and it looks phenomenal. Instead of a sponge, used some molded Styrofoam rings which I cut to make both an upper and lower lip. Upper gives it like a bill that keeps the fabric off your face, and put a dowel in the lower lip so I don't have to keep my arm up all day. Costume looks AMAZING. Great instructable!


1 year ago

I made this Sesame Street Martian costume with help from my respite care worker Marsha Newman. I wore the finished costume to an annual Halloween party and won the prize (a $25 Visa gift card that can be used anywhere) for best costume over all. Making a Halloween costume has advantages.


2 years ago

Thank you so much for this! But ... please help, I have two questions!! (I am not a normally crafty person, but my son saw this and just HAD to have it lol).

First question: For a 10-yr old kid who's not quite 5 feet tall, should I adjust the mouth opening to be smaller? The instructions say for it to be 21 inches high, but that would be way low on him, like down to his crotch. 16 inches high is down to his stomach ... can I use that instead?

And second question: I feel a little sheepish asking, but the person wearing the costume has to hold the mouth closed (grabbing the sponge) the entire time, right? If they let go, the mouth just gapes open?

Thank you so much, we're so excited about our Yip Yip to-be!!


3 years ago

Does anyone know if there is a video of this somewhere?


4 years ago

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4 years ago on Introduction

Unfortunately, the brand JoAnn's uses for curly fleece does not come in blue anymore. I will most likely resort to terry cloth. Also, did you know the Martians were improvised off of hats? Therefore, for a better look, mayhaps one should make the head hole circular?


4 years ago on Introduction

Oh my god, I love the aliens! Do you remember the one that goes,
"Ra-di-o!"? You did a fabulous job, and thank goodness the kids went
for it! It's uncanny how much it looks like the yip yips. :)


6 years ago on Step 8

on the previous step i noted the fragile state of our eyes, so what ended up working for us here was to hot glue (on low temp setting) the eyes to the antenna. we created a little semi-circle, c-shaped, base with the end of the pipe cleaner, and set the eye on top, secured with the glue. then we trailed the antenna up the back and secured the antenna with sewing pins criss crossed into the eyes. liquid nails would also work better for this. we hot glued (high setting) the base portion we created with the pipe cleaner to the top of the head and put some extra glue around the bottom to kind of "seal" it. then we just shaped the antenna out. they held all night.


6 years ago on Step 7

we had quite a time trying to attach our eyes. the hot glue was just melting the styrofoam. we tried tape and super glue also, with no success. on one, (due to damage between the eyes caused by the hot glue) we ended up using liquid nails, which kept them pretty damn solid all throughout the night. on the other costume, there wasn't as much damage, so i used a tooth pick to connect them (half the tooth pick in each eye) in the center and just put a little of the liquid nails in between, just in case.


6 years ago on Step 6

Can you clarify where you suggest pinning the weight to weigh down the mouth?

Is it attached to the approximate center of the black fabric?


6 years ago

Can't wait to make these....

I LOVE this costume idea! My boyfriend wants to make this to celebrate 'carneval' in the Netherlands, can't wait untill february!


7 years ago on Introduction

I made these for my daughter and her best friend this year. People loved them!! We used half a styrofoam ring on the inside for the mouth, regular fleece, and those gigantic pipe cleaners for the antennae. We bought 6 yards for each costume and had a lot left over. We used two layers of chiffon for the mouth and they ripped one off, after it got dark, so they could see. This was a toasty warm/dry costume too, which was good, since it was a cold, wet Halloween.
It's a costume, it's a muppet, it's awesome. :)


7 years ago on Introduction

My husband and I just got home from a Halloween costume contest. I still can't believe it - we took first place!

People loved the costume, but I think they loved the act more. We walked around the bar several times, looking things up in our book, yipping at people, and letting them take pictures with us. There were some pretty elaborate costumes, but ours had the most character.

Thanks so much for your awesome instructable. You helped us turn our idea into reality!


8 years ago on Introduction

Here's my attempt at the Yip Yips. My neighbor and I worked on these in one night. It took about 4.5 - 5 hours.

It was also insanely expensive. Not many places sell the curly fleece anymore, and the one place we could find (JoAnn Fabrics), only had it in one bright color, red. The rest of the colors were off-white, white, brown, and spotted, so they weren't exactly traditional Muppet colors. We purchased the red curly fleece (at $75 for 6 yards) and then opted for a cheaper, yet similar material in pink ($45 for 6 yards). I would strongly recommend using a cheaper material like Crushed Panne Velvet. It comes in a variety of colors and is more breathable. The only downside is that it doesn't hide pins, glue, etc. as well as the curly fleece.

In the end, the effort and money spent were pretty well worth it. People were beyond giddy at the reference (if they got it...we got a lot of "Elmo!" and "Hey Cookie Monster!" too) and were amazed we made them ourselves. My only regret was not enrolling ourselves in a costume contest or 2. Given the cost of the costumes though, I plan on using this for many a costume party and Halloween for years to come. Thanks for this Instructable!


8 years ago on Introduction

Me and my friend Anjali made these for halloween! We are both 12 and we know the yip yips because my dad used to watch them when he was little! :) I would upload a pic but I don't have one on THIS computer, hopefully somtime I will be able to uplad it! Thank instructables!! (: