# How much foam is required to fully absorb the impact of dropping a barbell?

I’m working on a project for my home gym. I want to be able to drop a loaded barbell without bothering my downstairs neighbors. My main approach is to use 2 blocks of dense foam on which to drop the barbell (when loaded with weights, barbells have 2 contact points to the ground). Ideally the foam absorbs the full impact of the weights, letting no vibration travel through the the floor.

I’ve learned that dense foam is expensive! A 4” tall block of decent foam costs \$106.

To help me determine what material to buy, is there an equation that calculates how much force foam of a given density and thickness can absorb, without any force passing through to the floor?

Some initial values:

• Assume barbell weighs 250 lbs, so 125 lbs dropping on each foam block
• Barbell is dropped from 72 inches above foam.
• Foam comes in densities of 0-8 lbs per cubic ft, escalating in price substantially.
• The contact point between barbell and foam pad is the width of the weight plates, an average of 7 square inches.

I’m looking for a way to find the optimal trade off between foam density and thickness. For example, a dense foam costs more, but requires less volume to absorb impact.

Thanks for any assistance!

• Read the small print at the bottom of the link: "Please handle with care as foam may tear when being handled due to its weight." If this stuff is liable to tear under its own weight, how many times do you think you can drop a 250lb weight on it from a height of 6 feet before it disintegrates? My guess would be "once, if you get lucky". – alephzero Apr 19 at 2:13
• Far easier not to drop them... – Solar Mike Apr 19 at 2:32
• 72” drop that stops in 4” is equal to 18 g’s and assuming 125 lb/7sq.in. * 18g = 321 psi density , which if walking on with 200 lb / 40 sq.in soles will depress only 5 psi/ 321 psi or 15 thou. So consider something almost as stiff as tire treads – Tony Stewart Sunnyskyguy EE75 May 22 at 0:10

Even if the foam does absorb most of the impact, it's going to get damaged.

You could try a sheet of plywood on top of the foam. Not only would it take the damage, it would distribute the energy over more of the foam.

Or you could even try multiple layers:

— barbell
— plywood
— foam
— plywood
— foam
— floor


You might be able to get away with relatively thin layers of foam.

(Though I suspect that eventually you'll end up damaging either the floor or yourself.)

Calculate the kinetic energy of the barbell before falling and get more info on the foam. When it deforms, how much energy does it absorb? That's a paremeter called resilience [J/mm3]. Search that parameter first or get data from similar or generic foams.

No foam or any rubber gym mat will be able to help you.

Too much weight to drop 6 feet.

You just have to lower your weight gently with the help of a friend spotting you on a steel frame with as many grab steps as your workout possibly requires.

That frame should be supported on a gym hard rubber sheet. like everyone who works out at home.

You could even be held liable for structural or property damage.