Elizabethan collars are clear plastic cones placed over the head of an animal in order to prevent them from scratching or licking a wound (see 3rd picture). Although E-collars are effective they can also cause the animal a lot of stress. E-collars limit peripheral vision causing the animal to run into a lot of things and also make it harder to eat and drink. This instructable offers an alternative that is cheap, easy to make, and will work in most of the situations that one would use an E-collar.
Warning: This collar is designed to give an animal more freedom than an E-collar and therefore cannot be used in every situation that an E-collar is used. In particular, it may not prevent an animal from licking/biting its front paws or the end of its tail. However, with cats (and some short faced dogs) it will prevent the animal from using its front paws to scratch its face. In any case, you should always watch your pet for a while to make sure this collar works as intended.
Step 1: Materials
1. Foam pipe insulation: This is the insulation used to keep pipes from freezing in winter. It should be fairly ridged foam and should defiantly not be fiberglass. What matters most is the outer diameter (O.D.). However, insulation is generally measured by the inner diameter so take a measuring tape. For my small to mid-sized cats I used foam with an O.D. of 5cm (2in). This size prevented one cat from licking or biting her hindquarters and prevented another cat from scratching her chin. For a large cat you should have 6 cm foam. A large dog would likely need foam with an O.D. of 10 to 15cm.
For large dogs you may want to fill the inside of the foam with cloth or smaller diameter foam so the dog can't simply crush the collar.
2. Electric or other plastic tape. The kind of tape you use is important as the collar is inevitably going to have contact with whatever your pet eats and drinks. I tried cloth athletic tape first and within a couple of days I had to negotiate terms with the colonies of bacteria that had seized control of the collar.
3. Shoelace, or other thick piece of string.
Step 2: Measure and Cut the Foam
Figuring out how much foam to use is a little tricky. I recommend overestimating as it is very easy to remove excess insulation but basically impossible to add insulation.
To calculate the length of foam you need the O.D. of the whole collar. The first step is to determine the diameter of your pet's neck. If your vet gave you an E-collar, you can use this to estimate the diameter, otherwise wrap your fingers around your pet's neck and guesstimate the diameter (Note: fur doesn't count). Again, overestimating is better than underestimating. The O.D. of the collar is attained by adding the diameter of your pet's neck to twice the O.D. of the insulation (e.g O.D. of foam = 5cm, diameter of neck = 6cm. 6+2*5=16. So the outside diameter of the whole collar will be 16cm.). The length of insulation will be the O.D. of the whole collar * Pi (e.g. 16cm * 3.14 = 50.24cm).
Step 3: Shaping the Insulation
In order for the foam to bend into a circle, you need to remove material from the inside of the foam. The easiest way to do this is to create a sawtooth pattern in the foam (see first picture). In this case it is better to remove too much than too little as the tape will cover excess gaps.
The first picture is much clearer than the description so look at that before you read on. First, draw a straight line down the insulation. Then draw another line 90 degrees (1/4 of the circle) from the first. The material to be removed will be equilateral triangles with a base that is the radius, r (i.e. 1/2 the diameter) of the O.D. of the insulation. To do this, use a ruler to place a mark every r centimeters along one of the lines. Do the same for the other line, except shifting each mark by 1/2 r (i.e. 1/4 the O.D.). Then connect the dots to make triangles.
When you are done marking the triangles, cut them out (second picture).
Finally, test that it bends properly (third picture).
Step 4: Add String and Test
Pass the string through the inside of the insulation. Then place it around your pets neck. Tighten the string until the insulation is tight enough that the animal can't remove the collar. If that is impossible, then you need to shorten the insulation.
Step 5: Tape It Up
When you get the right length it is time to tape it up. The primary purpose of the tape is to maintain the circular shape of the collar. The secondary purpose is to give the collar an easy to clean surface. I started with a little duct tape to hold the basic shape, then wrapped the entire thing in electrical tape to make it easy to clean. I initially tried cloth athletic tape, but that simply absorbed food, water, medication, blood, and anything else that happened to touch it.
After the collar is taped poke a couple of small holes along the outside near each end (see picture). Then pass the string through these holes. This allows you to tighten the collar a little more than if you left the string in the center of the insulation.
You can wipe the collar once a day with a little rubbing alcohol to keep it clean.