the Definitive Guide to the
COBRA BAG

by Reedy Kewlus

What is a Cobra Bag?

The cobra bag is a type of reflex punching bag that incorporates a football-sized ball on top of a rod or pole that is able to flex back and forth. It's generally configured to be at chin level, and when punched, designed to return to the user's chin simulating a counter punch. There are two types of cobra bags: one type that uses a spring to flex; and the other that uses a flexible rod. There are also many subtle differences that are outlined in the Anatomy of a Cobra Bag section below.

Why a Cobra Bag?

The cobra bag is one of the best training tools that a boxer can have to develop a high level of hand-eye coordination and defensive reflexes. The interactive nature of the cobra bag makes it fun to train with. Even if you're not into boxing, but simply want a fun, interactive and challenging way to exercise your whole body, the cobra bag will give you that and more.

Here are some of the key reasons for using a cobra bag in your training routine:

It's fun. It's fun because it is interactive and will punish you if you don't keep your eyes on the ball and dodge it when it comes back at you.
It works out all the key muscle groups in your body, especially your shoulders, core and legs as you need to punch the bag, then move side to side to avoid getting hit.
The bag motivates the user to sustain the rhythmic motion, thus encouraging a prolonged cardio workout. In combination with background music that closely matches the rhythm of the bag it can make for a fun and highly motivating cardio workout. Just 3 x 3-minute rounds with 30 second breaks will give you a workout equivalent to an hour on the treadmill.
It teaches key self defence principals and over time generates muscle memory for moving side to side in order to avoid getting hit.
It's easy to set up, and with some designs like the modular Kewlus Cobra Bag Kit it's also easy to put away after each use, making it accessible to every home and not just the gym.

Types of Cobra Bags

There are two types of cobra bags: one type that uses a spring to flex; and the other that uses a flexible rod. The most common of the two is the spring-based cobra bag.

Spring-Based Cobra Bag

The spring-based cobra bag uses a spring for the flexing action of the mast. These are further divided into two sub-categories:

Spring positioned at the bottom of the mast - this is an entry level type of cobra bag ideal for someone who is starting off as the back and forth movement of the bag is relatively slow. These are quite inexpensive and can be purchased for under $50 at stores like Kmart.
Spring positioned mid way along the mast, roughly at user's hip level - this is the more advanced version of the two, with faster rebound action. These range in price from around $100 up to $800 plus shipping.

Check out the Spring Based Cobra Bag DIY post for a great example of such a cobra bag.

Flexible Rod Cobra Bag

The second type of cobra bag uses a flexible rod for its mast, thus dispensing the need of a spring. The dynamics are very similar to a spring-based cobra bag with one key difference: There is no single flex point like with a spring, but rather the whole mast flexes, which extends the reach of the cobra bag slightly beyond that of a spring-based version.

Check out the PVC Pipe Cobra Bag DIY post for a great example of such a cobra bag.

Anatomy of a Cobra Bag

The key components of a cobra bag from the top down include the ball, the mast and the base. Most cobra bags come pre-assembled, while others require some assembly. The Kewlus Cobra Bag is a modular design, where all the components simply click together. The Modular Cobra Bag section below outline some of the advantages of a modular design.

The Ball

The characteristics of the ball of the cobra bag will affect the dynamics of the rebound as well as the longevity of the bag.

At the lower end, the balls are made from synthetic materials that generally will not last with regular use. Some are quite large and somewhat soft, targeted towards beginners. Others are made from solid rubber, making the ball quite heavy and greatly reducing the rebound speed.

The ideal cobra bag ball should be around the size and shape of a standard speed bag. In general, the smaller and lighter the ball, the faster it will rebound. However making it too small can take away from the satisfaction of hitting something solid.

The materials used in making the ball (eg. durable and lightweight) as well as the design and craftsmanship (eg. ball shape and stitching) are important in achieving the optimum performance and longevity of the cobra bag.

The Mast

The anatomy of the mast will depend on the type of cobra bag. In the case of a flexible rod the mast will mostly be a long flexible rod. In the case of a spring-based cobra bag, the mast will consist of a short metal tube/pipe on which a spring is mounted. The top end of the spring will be connected to rod or tube on which the ball is mounted. In most cobra bags the height of the cobra bag is able to be adjusted via the mast.

The Base

The base is probably the most important component of the cobra bag as it needs to be rock solid and sturdy to allow the bag to flex back and forth. The heavier the bag and the harder the punches, the greater the forces imposed on the base.

Cheaper versions of the cobra bag use a water filled base and position the spring at the very bottom of the mast to reduce the applied forces. There are two main cons of a water-filled base: hard to move after it is filled; and a risk of splitting and incurring water damage. Water filled bases also don't allow for the cobra bag to be shortened low enough for kids due to the high anchor point of the mast.

The Kewlus Multi Base give the user a choice of base options, from being able to use suction cups on tiled floors, to screwing it to a wooden deck or concrete slab, to using it with a baseboard or Platform Paddles weighed down by two 45 pound (20kg) sand bags. In a home environment, it's a lot easier to put away two 45 pound sandbags with handles than having to drag a 90 pound water container.

For spring-based cobra bags, especially where the spring is mid-way or hip level, the rigidity of the base is crucial. Minor flexing in the base will result in dampening of the rebound motion of the bag.

The Modular Cobra Bag

My own latest concept is to have a modular cobra bag where components can be interchanged, upgraded and modified by the user. For example, the ability to switch from a small ball to a larger one, or from a lightweight spring to a heavyweight one, gives the user greater variation in their training as the dynamics of the bag change.

This opens up the capability to integrate DIY components to further enhance or customise the cobra bag. It allows users to also save money by substituting some of the components with off-the-shelf parts such as 3/4 inch pipes from a hardware store at a fraction of the cost.

Being modular also means that when a component breaks long after the warranty has expired, it's very easy and cheap to replace it.

Cobra Bag Training

Training with a cobra bag is a lot of fun because of the interactivity and constant movement. The cobra bag is a great motivator because once you establish a rhythm, you just want to keep going. I have put together a number of training videos that you can follow to help you train with a cobra bag. From how to get started to more advanced sessions. Click Here to get started.

Let me know below if there's anything I missed or anything I should add to this page or to my training videos. Have Fun!

Cobra Bag DIY (Do It Yourself)

Getting a good cobra bag doesn't have to be costly. If you like making things then you can make a cobra bag for relatively little money. One of the lowest cost and best performing DIY cobra bags that I made was a fishing rod version. Yep, a cobra bag made from an old fishing rod - and it works great!

Check out my YouTube channel as well as the DIY section of my main website for instructions on how to make all kinds of cobra bags. I have made it easier for you to make DIY cobra bags like a spring version or a PVC pipe version by providing some of the components that you would not normally get in a shop, such as dedicated cobra bag spring.