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Foam gun vs straw: three ways to get the foam out

Updated: 23 October 2026

The shelf offers a straw can, a Soudal Genius Gun can, and a separate screw-on foam gun. They are not the same tool. A foam gun vs straw choice goes wrong when you buy the gun for a single small hole, or when you try to screw a straw can onto the basket. This page says when each format earns its place. It does not rank the eleven guns. Peter F. used Penosil, Soudal and the amazon.co.uk capture of 19 October 2026. This is not a lab test. A qualifying purchase can earn us a commission at no extra cost to you. The guns are on the [foam gun comparison](/hub/fillers-adhesives-and-sprays/foam-gun).

The shelf offers a straw can, a Soudal Genius Gun can, and a separate screw-on foam gun. They are not the same tool.

Our top picks

fischer fischer PUP M3 metal foam gun

Best overall

fischer fischer PUP M3 metal foam gun
8.6/10about £19.84
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Lytool Lytool PU expanding foam gun

Best value

Lytool Lytool PU expanding foam gun
8.1/10about £14.29
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Grapelet Grapelet PU foam gun

Rank 3

Grapelet Grapelet PU foam gun
6.8/10about £8.99
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On this page
  1. 1.Three ways to get the foam out
  2. 2.Control and how much the foam grows
  3. 3.What else you have to buy
  4. 4.When a gun is the wrong buy

Three ways to get the foam out

A straw can is the hand-held aerosol. You shake it, fit the tube, and the can is the applicator. A Genius Gun can is Soudal's hand-held format. The trigger is on the can, and the straw is meant to reseal, with reuse of up to six weeks. It is not a screw-on canister for the guns in this set. A screw-on gun meters gun-grade foam. The can sits in a basket, a rear screw sets the flow, and the trigger lays the bead. It needs a gun-grade can and, if that can will come off, a cleaner. Builders Hardware Direct states that gun-grade and hand-held cans are not interchangeable. The wrong can pours foam at the collar.

Control and how much the foam grows

Straw foam keeps expanding after it leaves the tube. Penosil caps a straw joint at about 50 per cent and aims gun foam at windows and doors, filled to about 60 to 70 per cent. Soudal puts hand-held foam and the Genius Gun at a lower fill because they expand more after they leave the nozzle. The can in your hand is the instruction. The bead sequence is on how to use a foam gun.
fischer fischer PUP M3 metal foam gun

Testsieger

fischer fischer PUP M3 metal foam gun
8.6/10about £19.84
View offer

What else you have to buy

A straw can is one purchase. A Genius Gun can is also one purchase on Soudal's description: no separate gun and no gun cleaner. A screw-on gun adds the tool and, if the can will come off, a cleaner. On this capture the guns run from about £8.99 to about £23.99, and every box omits the foam and the cleaner. Cleaner only dissolves foam that is still wet. Thread and seal are on the foam gun buying guide.

When a gun is the wrong buy

Buy a straw can, or a Genius Gun can, when the job is one small gap you will finish today. Buy the gun, a gun-grade can and a cleaner when you have several frames. A fire door, a flue, a fire-stopping line, a frame that has moved, and a specified cavity need the product the design names. If you are already sensitised to isocyanates, do not take the job on.

Common questions

Is a foam gun better than a straw can?
It is better when you need a metered bead and lower post-expansion, which is the usual case for several window or door frames. It is the wrong buy for one small gap you will finish and forget. Straw foam is simpler and expands more after it leaves the tube, so Penosil caps that fill at about 50 per cent. A gun also means a gun-grade can and a cleaner.
Will my old straw can fit the gun?
No. A straw can does not screw onto these baskets. Builders Hardware Direct states that hand-held and gun-grade cans are not interchangeable. Forcing the straw can on is how foam pours at the collar. Buy a gun-grade canister for the gun, and keep the straw can for a job that uses its own tube.
What is a Genius Gun, and does it need these guns?
A Genius Gun is Soudal's hand-held can with its own trigger and a straw the maker says you can reseal for up to six weeks. It does not need, and does not fit, the screw-on guns in this set. Soudal groups its expansion with hand-held foam, about 30 to 40 per cent fill, not with gun-grade foam. It is a third format, not a cheaper foam gun.
How much extra do I buy if I choose a gun?
On this capture the gun is about £8.99 to about £23.99, and the box contains neither foam nor cleaner. You still buy a gun-grade can, and you buy cleaner if the can will come off. A straw or Genius purchase is the can alone. A guide price of about £20 for a basic gun is other publishers' context, not the price of a named ASIN here.
Which expands more, straw or gun foam?
Straw and Genius foams expand more after they leave the nozzle. Soudal puts that expansion at about 150 to 200 per cent, against about 50 to 100 per cent for gun-grade foam. Straw fills stay lower: about 50 per cent on Penosil's guide and about 30 to 40 per cent in Soudal's FAQ. Gun fills in those sources sit at at least 50 per cent, about two thirds, 65 per cent, or 60 to 70 per cent. Read your can.
Is a gun worth it for one window?
Often no, if the window is a single small gap and you will not foam anything else this month. A straw or Genius can is the smaller commitment. A gun is worth it when that window is one of several frames, or when you need to pause the bead and keep the rest of a gun-grade can on the tool. Either way, overfilling can still bow a frame.
Can I reuse a straw can the way I reuse a gun?
Not in the same way. A straw tube often blocks once you start, and the rest of the can is lost. Soudal's Genius Gun is the hand-held exception they advertise as resealable for up to six weeks, and it still is not a screw-on gun. A separate gun reuses the tool only if you leave the can on or flush with cleaner. The choice does not change for a fire door: none of these formats is a tested fire seal.

Related pages

How to clean a foam gun

Foam gun

Best foam gun: the top pick, value, and who to skip

Foam gun buying guide: thread, cleaner and reviews

How to use a foam gun without packing the gap flush

Sources

Public UK sources used for this comparison. amazon.co.uk prices, stars and review counts were taken from the listings on 19 October 2026.

  1. HSE, Isocyanates (retrieved 19 October 2026)
  2. HSE, occupational asthma substances (retrieved 19 October 2026)
  3. Penosil UK, straw foams vs gun foams (retrieved 19 October 2026)
  4. Screwfix, how to use an expanding foam gun (retrieved 19 October 2026)
  5. Soudal UK, storing an opened can (retrieved 19 October 2026)
  6. Soudal Gun & Foamcleaner TDS (retrieved 19 October 2026)
  7. fischer UK, PUP M3 33208 (retrieved 19 October 2026)
  8. Environment Agency aerosol canister guidance (retrieved 19 October 2026)