Flexible Force Field
(Evocation)

Range:  10 yards
Components:  V, S, M
Duration:  Permanent
Casting Time:  1 round
Area of Effect:  10 square feet per level
Saving Throw:  Negates

This spell creates an invisible barrier in a space desired by the caster. It cannot stand by itself - all edges of the flexible force field have to touch something solid, although if movement later would cause these edges to expand or contract, the field will expand or contract to allow for this to its maximum area of effect (further expansion will dispel the wall). The flexible force field can have a living being as part of an edge, but if so that being gets a saving throw versus death magic, success indicating that the field is dispelled. Failure means only that the being is an edge - it does not stop that being from moving around, which could soon cause the collapse of the spell. A flexible force field will allow only the following to pass: gas of all forms (including air), creatures able to move under their own volition, objects held or worn by these creatures, and light.
Note that sound will also pass through the field, being transmitted by air. Hence, animate plants, animals, (virtually all) monsters, undead and even insects can move through the field, but water, dirt, molten magma and even spells (except those mentioned below) cannot pass through unaided. A crossbow bolt would stop dead upon hitting the flexible force field, whereas a mosquito would fly right through it. The field will generally last until destroyed by a force that could remove a wall of force, for example disintegrate, limited wish, wish and the like, as well as by stretching it too far, as discussed above. Otherwise, it will last indefinitely. Note that although spells cannot pass through the field, they might create effects which can. For example, shout or sunburst will be effective through the field as it transmits sound and light, and summoned creatures will be able to pass through it.
The exact shape of a flexible force field is not subject to the whims of the caster - it will form so that the least area is needed to contact all the outside surfaces - like a soap bubble. Being a form of pure magic, the field cannot be coloured or painted to disguise its true form. However, the only clue of its existence is a faint blue glimmer, which is only 40% detectable unless looking for it (in which case this rises to 80%, roll once per round for each searcher). These percentages are halved if the flexible force field is at the boundary of substance with a blue colour - for example, underwater, separating an air pocket from the sea. The material component is at least 500 gp worth of powdered diamond (under standard Player's Handbook or Dungeon Master's Guide prices - this could be less near a diamond mine, or more in a forest community, depending upon the DM). This dust must be sprinkled over at least part of each surface that has to form as an edge for the flexible force field. For example, if this was a mouth of a tunnel then dumping the whole lot at the bottom of the mouth would do, whereas the average constructed doorway would need a dab on both sides as well as the top and bottom, being made up of four pieces of wood joined together.

