A better starting layer.
100% merino wool in the boxer body. Natural rubber at the waist. A deliberate choice, every day.
Cooling underwear. A different standard.
Stop cooking
in plastic.
Your future deserves attention. Start with sperm health and the everyday heat you can address.
Product visualisation
The founder offer
Cooling Boxer + Inserts
$69.00
1 merino boxer · 2 reusable cooling inserts · No extras
One payment today. No subscription.Full refund before it ships.
Target dispatch: 30 September 2026. Subject to final production confirmation.
Not ready to pre-order? Keep me in the loop.
Get founder updates and a heads-up about the first drop.
100% merino boxerCentred merino sleeveNatural-rubber waistbandTwo reusable inserts
Built from the inside out
Natural where
it counts.
You watch your diet, sleep and training. What about the layer you wear all day?
Cooling, in the centre.
The merino sleeve holds the insert in the centre, separate from your skin.
Two inserts. Used again.
Reusable inserts absorb body heat as they soften. No refills or subscription.
The research that started the conversation
The numbers should
get your attention.
51.6%
Decline in mean sperm concentration.
A global meta-regression estimated a 51.6% decline among men unselected by fertility status between 1973 and 2018. It did not establish that underwear or heat caused that trend.
Levine et al. · Human Reproduction Update+2.6–2.8°C
Scrotal temperature rise in 60 minutes.
In a study of 29 men, a working laptop on the lap produced this measured rise. Posture contributed too: the same sitting position without a laptop raised temperature by 2.1°C.
Sheynkin et al. · Human ReproductionResearch context: these studies did not test NUMBNUTS and do not prove that it improves fertility. They explain why we pay attention to heat, rather than establish a product outcome.
You cannot change a global trend. You can start with your everyday habits.
Five questions turn your reported heat and fabric habits into a clear starting point. The Heat Check does not measure sperm or diagnose fertility.
An everyday routine, simplified
Wear it. Place it.
Get on with it.
Start with the boxer.
Pull on the merino boxer as your everyday base layer.
Use the centre sleeve.
Place a fully solid insert inside the centred merino sleeve.
Remove. Reset. Repeat.
Remove after your session. Follow the supplied reset and care instructions before reuse.
Never place an insert directly on skin. Remove inserts before sleeping. Final reset and care instructions accompany the production product.
See the idea in motion
An upgrade for your everyday.
The NUMBNUTS product film. A closer look at the idea behind the first drop.
The founder promise
Get in early.
Keep your options.
The first drop should earn its place in your drawer. A simple offer, clear terms and the option to cancel before it ships.
Jaspal RaiFounder, NUMBNUTS
A preorder. Clear from the start.
Pay today for one boxer and two reusable inserts from the first production drop. No automatic repeat charge.
60-day first-pair guarantee
Cancel for a full refund before fulfilment. After delivery, try your first one-boxer/two-insert bundle for 60 days. Not for you? Get the bundle price back, with no worn return required. One first-pair claim per customer; see full terms. Read the terms
UK and US delivery.
Currently delivering to the UK and US. Delivery is free on orders of US$65 or more, or the local-currency equivalent. Any applicable charges are shown at checkout. Target dispatch: 30 September 2026. Subject to final production confirmation.
What exactly comes in the first drop?
One 100% merino wool boxer with a centred merino-wool sleeve and natural-rubber waistband, plus two reusable cooling inserts. No case or extra accessories.
How do the cooling inserts work?
A fully solid insert absorbs body heat as it softens. The merino sleeve holds it in place. Follow the supplied instructions to reset and care for it between sessions.
How do I choose my size?
Use the waist measurements in the size guide. The cut is designed to be loose; if you are between sizes, size up for a looser fit.
When will my preorder ship?
Target dispatch: 30 September 2026. Subject to final production confirmation. You'll receive updates as the first drop progresses. We currently deliver to the UK and US. Orders of US$65 or more, or the local-currency equivalent, qualify for free delivery; any charges are shown at checkout. Read the terms
What if I change my mind?
Cancel for a full refund before fulfilment. After delivery, try your first one-boxer/two-insert bundle for 60 days. Not for you? Get the bundle price back, with no worn return required. One first-pair claim per customer; see full terms. Read the terms
Will NUMBNUTS improve my fertility?
We do not yet have clinical evidence showing that NUMBNUTS improves sperm quality, pregnancy rates or fertility. The published research explains why heat deserves attention, not a promised product result.
