How to Choose Thermal Pad Thickness - The Practical Way

Choosing pad thickness causes more confusion than anything else we sell - and most of the advice online skips the part that actually matters: pads compress, and harder pads compress less.
This is how I work it out on the bench, with a plastic ruler and no lab equipment.

Measuring the old pad

You don't need calipers - a plastic ruler is good enough. Old pads are usually slightly bigger than the component they sit on, so part of the pad is often not squashed at all: measure that edge. If it reads "1mm and a bit", it was almost certainly a 1.5mm pad; if it's under 1mm, it was probably 0.5mm.

If the whole pad is squashed, measure the squashed thickness and add roughly a quarter, then round up to the nearest standard size. A pad squashed to 1.1mm was a 1.5mm pad; squashed to around 1.5mm, it was most likely 2mm.

Pads compress — and hardness decides how much

This is the bit that matters. Under normal mounting pressure, for the pads we sell:

• 8W pads are the softest - they compress to roughly 60–70% of their original thickness

• 12.8W pads are medium - roughly 70–80%

• 15W pads are the hardest - roughly 75–85%
  

(Generic pads at the same W rating can behave differently — these figures are for our stock.)

So a 1.5mm soft pad and a 1.5mm hard pad do not end up the same thickness once the heatsink is screwed down. Which leads to the mistake almost everyone makes:

Upgrading to a harder pad? Go thinner.

Most mainstream GPUs and laptops ship with pads somewhere around 3-8W some stock pads are rated even lower. Upgrading to 12.8W or 15W works well - but if you fit the harder pad in the same thickness as the old soft one, it won't compress as far. The result is constant pressure on the board and components that the manufacturer never designed for, and in the worst case the die itself loses proper contact with the heatsink because the pads are holding it off.

The rule: when you go firmer, go down a size to compensate. An 8W 1.5mm pad is often best replaced with a 15W pad at 1.25mm or 1mm, depending on the gap. Work from the compressed thickness, not the number on the packet.

Cutting and handling

Scissors are the wrong tool - they squash the pad edge as they cut. Use a wallpaper knife, a bare blade or a scalpel with a ruler. Two easy methods: lay the old pad on top of the new one and cut around it, or draw the lines on the protective film and cut along them.

We also sell pre-cut pads sized for GPU memory - the height is already right, so you only cut the length.

Handling: gloves, or dip your fingertips in isopropanol to take the grease off and just use your fingers. I can already hear someone saying that's not the proper way - of course it isn't, and in real life it makes no difference.

Reusing old pads

Fine, as long as they're not dried out or falling to bits. A pad in good condition goes back in.

Pads or putty?

Don't overthink it: replace what was there with the same type. My one rule - you can replace pads with putty, but never putty with pads. Manufacturers use putty where a pad would be too thin or too thick to work, so if you find putty, putty goes back in. For consoles and laptops, putty up to about 10W is right for normal use; the very high-conductivity putties need the amount adjusting and aren't worth the complication for a standard repair.

What you'll need for this job

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Thermal pads — 8W to 15W/mK

Odd gaps: 0.75mm, 1.25mm, 1.75mm

Plenty of GPU and laptop manufacturers use in-between pad sizes - 0.75mm, 1.25mm, 1.75mm - while most pad brands only sell 0.5mm steps. Three ways to handle it:

1. Use the exact size. Our Fehonda pads come in the in-between thicknesses too - 0.75, 1.25, 1.75, 2.25 and 2.75mm so you can simply replace like for like. Have a look through the store.

2. Go one step up - soft pads only. A soft 8W pad one size above the gap compresses down into it: 1mm for a 0.75mm gap, 1.5mm for 1.25mm. This trick does not work with 12.8W or 15W pads — they barely compress, so sized up they hold the heatsink off the die, and sized down they don't reach across the gap. For the firmer grades, use the exact in-between size or putty.

3. Use putty for the really awkward spots — it takes whatever shape the gap has.