First of all, hi and thanks for reading. Secondly, it’s an involved question that needs an answer divided into two parts.

 The bottom line

 All the gushy details technical details of what gold filled is.

First, the bottom line. 

• 14/20 gold filled is less allergenic and less irritating to the ears.
• Will last and shine for much longer than gold plated jewelry since it is made of up to a thousand times more gold bonded strongly to the inner metal.

Second, the gushy technical details.

Below is a brief synopsis of the difference between them. There is a lot to this and this post will be updated from time to time with more info until it is finished. 

GOLD PLATED

Gold-plated jewelry is created using an electro-chemical process that places a layer of Gold on copper, brass, or some other base metal.  The thickness of the Gold used in plating usually no more than a few microns (that’s really thin). The gold layer (and hence the gold color) will wear off at varying speeds due to a variety of factors. These include, the wearer’s skin salts, elements or moisture in the air or pollutants in the air, exposure to the air, and of course, if you happen to have an electroplating rectifier you can easily remove all the gold plating on your jewelry should you so choose. The thinness of the layer of gold can also cause an allergic reaction to the wearer. The percentage of people who experience an allergic reaction to gold filled is significantly smaller than those who experience a reaction to gold plated.

GOLD FILLED

Gold-filled jewelry is created by using heat and pressure to bond a solid layer of Karat Gold to  copper, brass, or some other base metal.  The amount of gold is sometimes hundreds of times more than in a comparable gold plated piece. The bond produced is much more permanent and the allergic reaction ratio is much lower than that of gold plated.

Gold filled pieces can NOT be casted as base metal and pure precious metals can. Due to the manufacturing process, it is not always possible to get the same versatility in design as these other metals. However, gold filled jewelry does offer significantly more design opportunity and size as compared to 14k gold and as such is often seen as a great middle of the road for the consumer. With reasonable care, gold filled jewelry will last a lifetime.