Question Spirits in the material world

If they are summoned into a properly made circle, they can be as solid as they want to be... because that's one of those rules about properly made circles : they obey the rules defined by the circle being raised, not the reality on the outside. Inside a circle, a spirit or elemental or dimensional being... can operate as if they are 'back home'.

However, outside a circle, they're in the physical world... where everything non-material takes energy to be made material and sustain 'life'. Thus why things from 'outside' like hallows (avatar or otherwise)... because they are places where the rules are relaxed some, and it costs less to sustain oneself in the world. Anything else? Costs. Visibility? Costs. Material form? Costs. And going home? That's not free either.

In most cases, that will be part of the contract and 'cost' of summoning. The caster commits to protecting and sending the spirit or elemental home. It, on the other hand, is responsible for doing whatever it is that the contract called it for. If a Fire Elemental is brought over to be a combatant, its probably going to manifest as flame under its own power... because doing flame is its thing. No Earth-born mage is going to do fire as well as an Elemental from the plane of Fire. But if the mage wants the elemental to spend its time as a flame in a lantern until an intruder comes in and the elemental is released to attack it? That might be on the caster to 'pay for'. Because that form needs to be sustained to keep the elemental here safely until it does its part.

Mostly, that Essence cost will come 'up front' because it will be bound into the contract. It might be possible for a mage to 'pay into' or 'renew' the contract along the way so its not all paid up front; but only a 'fool' would enter into a contract where the mage promises to pay 'after' service is rendered. Because that's a good way for a being from another world to get dead because they depleted themselves doing a job and then get stiffed on payment, and not have enough left to get home. So the contract itself is binding for more than just as an oath / honor thing. The contract holds the Essence to pay out (or punish) the entity when it accomplishes (or fails) to do as bound.

As to how 'physical' solid... that's going to depend on plenty of things, as Dan said... also... keep in mind that 'some' things are solid - an Earth Elemental will do solid easily. Some things... it's going to take a LOT more energy to make them solid. Air Elementals CAN be solid. But it takes a LOT more power to make Air solid. Or Fire.

whether they can be trapped by something that holds solids or not has little or nothing to do with the question, which was the energy required to manifest them physically (solidly). manifesting something that is inherently gaseous by nature (or is energy emitted through the release of chemical bonds)... is going to take more energy, because you are generating more of a 'shell' than you are when summoning something that is inherently 'rock' or metal... and in ALL cases... spirit or elemental... their 'sentience' or 'consciousness' is more the issue than what they are made of / their nature.

not saying you're wrong. just that its more than just a 'states of matter' thing. I know some contemporary folks like to impose modern science (states of matter) on the old ideas of the alchemical elements... and that's fine, from a real world chaos magick or contemporary eclectic perspective. but the WU has a far more visible magic tradition (including alchemy) and a real (publicly visible) history of elementals and spirits summoned from other worlds/planes... so you can't push too much "we've improved our understanding scientifically and replaced those old ideas" onto things.