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Gear 101: What is hot melt, and why is it used in Tour heads?

April 14, 2020

Some amateur golfers view hot melt — also known as “rat glue” — as the secret sauce that professional golfers and Tour club builders use to make drivers perform better. With that thought in mind, amateurs or home DIY-ers are eager to pump hot melt into their driver heads to be just like the pros. The problem is, without a complete understanding of the material, it’s extremely easy to incorrectly apply hot melt and irreversibly ruin your driver head.

To get a better understanding and hopefully avoid future disasters, let’s break down exactly what hot melt is, how it’s applied and why it’s used.

Hot melt is a thermoplastic adhesive that starts in a solid state, liquifies when heat is applied (usually by a hot glue gun), then dries and solidifies. The material is used for numerous purposes not involving golf, one being rat traps, thus nicknamed “rat glue.”

In the world of golf, hot melt has been used for years to add weight to driver heads, manipulate center of gravity (CG) for trajectory biases, to mute sound and improve feel.

Club builders apply the hot, liquified glue into the driver head, then tilt the driver head in order to get the liquid glue into a specified location before it dries. Once it’s dry, it’s very difficult to remove; that’s where amateur DIY-ers get into trouble.

One squirt of hot melt from the glue gun can produce a gram or more of weight. Keep in mind that just one or two grams can actually have a large influence on how the club feels and performs, so it’s easy to overdo it on the glue.

Many golfers think hot melt is exclusive to high-end club building, but actually, it’s possible that your stock retail driver already has hot melt in it! Some driver manufacturers put hot melt into stock heads as part of the manufacturing process to mute sound, get the correct weight, or use it as a catch-all for loose materials inside the crown.

Aside from that, the rumors about pro golfers using hot melt in their drivers — even in the modern era of adjustable drivers — are true. Since hot melt acts as a vibration dampener, nearly all pros use hot melt to reduce vibrations in their drivers, thus improving sound and feel.

Depending on the location of the hot melt, the material can also change CG. The same rules of lead tape apply with hot melt: glue in the front of the head will lower trajectory and spin, glue in the back of the head will raise launch and improve forgiveness, glue in the heel will influence a draw, and glue in the toe will influence a fade. Unlike lead tape, though, dried hot melt inside of a driver head isn’t going anywhere; while lead tape comes off easily, hot melt is more permanent.

Remember, pros and Tour-level club builders never just pump hot melt into a head for no purpose. They have a precise reason — such as dialing in a certain ball flight or feel — and they know exactly where they want the glue to be applied, and how much.

“Most amateurs perceive hot melt as this magical tool used by Tour club fitters to dial in the acoustics so that it’s more palpable for a Tour player,” says Tim Briand, Senior Vice President for GOLF.com’s sister company True Spec Golf. “I’ve seen a lot of amateurs who will dump hot melt into the head trying to change the way the club head sounds without any consideration for how that could radically change mass properties.”

Hopefully, after reading this article, you’re a bit more careful during your next hot melt driver experiment. The absolute best way to add hot melt into a driver is to consult a professional fitter or club builder. The next best way is to go slow, use less hot melt than you think, and keep a scale handy so you know exactly how much hot melt you’re applying.

To hear more gear insights from Jonathan Wall and True Spec’s Tim Briand, subscribe and listen each week to GOLF’s Fully Equipped podcast: iTunes | SoundCloud | Spotify | Stitcher