Hop Spider vs Hop Bag

The shared cost

Both reduce utilization, and that is honest

Start with what both options have in common: they restrict hop movement, and restricted hops extract less. Alpha acid isomerization depends on contact between hop matter and circulating wort, and a basket or a bag reduces that contact.

The loss is modest and it is real. Anyone selling containment as a free improvement is overselling it. What you are actually buying is equipment protection -- see best hop spiders for the full argument about why that matters.

Which means the first question is not spider or bag. It is whether you need containment at all: if you brew with an immersion chiller and no pump, free-floating hops cause you no equipment problems and you keep full utilization.

Where the spider wins

Absorbency and movement

It does not absorb. This is the strongest practical argument and the one people underrate. Nylon mesh takes up hop oils, stains, and carries aroma between batches. Brew a heavily hopped IPA in a bag and the next beer through the same bag starts with a hint of the last. A stainless screen has no absorbency at all -- it rinses clean and carries nothing.

It restricts movement less. A spider is a rigid basket with hops loose inside it, so wort circulates through the mass. A bag packed tight with the same weight of pellets compresses them into a dense plug, and wort flows around rather than through. On utilization, a loosely filled spider beats a tightly packed bag.

It lasts. Bags tear, stretch and eventually get thrown away. A stainless spider is a buy-once item.

Where bags win

Flexibility and dry hopping

Separate additions. A recipe with 60, 20, 10 and flameout additions is four bags you drop in on schedule and remove individually. A spider is one basket that accumulates everything, so your 60-minute hops sit in there until the end whether you want them to or not. For recipes with many timed additions, bags are genuinely more practical.

Dry hopping. A spider lives on the kettle rim and cannot go in a fermenter. A weighted mesh bag can, which makes it the tool for dry hopping in a vessel where you need to remove the hops later -- particularly relevant on a pressure-rated fermenter where you want to avoid opening it more than necessary.

Capacity by multiplication. A spider caps out around 8 to 10 ounces. Four bags can hold more total hops than one spider, each loosely filled, which addresses the heavily-hopped-IPA problem a spider has.

The third option

Filter at the pickup instead

There is an approach that avoids the utilization trade entirely: let the hops float free and filter at the point of exit with a kettle screen or a filter on the pump pickup.

Full extraction, nothing restricting the hops, and the debris gets caught on its way out. The cost is that a screen can clog during the transfer rather than preventing the problem upfront, which means stopping mid-transfer to clear it. Combined with a whirlpool -- letting the trub settle into a cone in the kettle center and transferring from the edge -- it works well, and it is what many brewers with a pump eventually settle on.