Molds are used for packing snow into a desired shape. Cassette molds designed for concrete constructions can be used for large wall-like structures. For smaller wall or sculpting structures, it is best to use molds made of plywood board or sheet metal, because packed snow comes off their surfaces quite easily. Molds made of boards or sheets must be supported with wood or steel structures to make it stand the weight of the snow and the pressure of packing.

Slipform casting construction is usually used for snow walls. This means leaving one end of a mold open and supporting it on the snow structure. The mold is moved forward as the construction advances.

Flexible molds made of fabric or plastic can also be used in snow construction. To make a pneumatic fabric mold, for example, a cloth bag is filled with compressed air. A band is put around the construction and dense snow is molded around it. After the snow has hardened, the compression is released and the fabric removed from inside the construction.

In designing snow constructions, structures that create tensile stress should be avoided. Walls, towers (which can either have the same diameter from one end to the other or grow thinner towards the top), arches, vaults, and domes are well-suited for snow structures. Other surface and exterior structures require exact calculations of pressures and transformations.

The minimum thickness for non-bearing walls is 0.3 meters, for load-bearing walls 0.5 meters, and for tall (>5m) vertical structures two meters. The arches of vaults and domes must span 0.3 meters and their bases must be one meter thick. When calculating solidity, it is important to bear in mind that sunshine and above-zero temperatures cause the surface to melt and become slushy: the thickness of the layer of slush must be subtracted from the thickness of the structures and added as load on the structure.

Small door and window holes (width < 1m) can be built as squares or rectangles, but for larger ones at least the top part should be arched to prevent pressure and sagging. Sagging can be prevented by packing snow very tightly around the hole so that the density can counteract the weakening effect. Furthermore, the number and placement of holes should be chosen so that the surface area of the bearers between the holes is enough to carry the weight. The width of these supports must be at least the same as the thickness of the structure. It is also important to bear in mind that unless sagging is taken into consideration, doors can get stuck and windows can break. Therefore, there should always be room for sagging on the top of the frame.

Reinforcement is one way of preventing sagging, but some things need to be taken into consideration. The materials used for reinforcement should be such that properly stick to snow. For example, in an arch where snow packs naturally, a net incorporated within the structure can prevent sagging. However, net structures can also be harmful by preventing snow crystals from binding with each other, thus leaving pockets of air in the structures and causing pieces to chip off.

Instead of reinforcement, another solution is to make structures lighter. Snow structures such as tall towers can become so heavy that they buckle under their own weight. Sunshine and wind can also cause a structure to start leaning on one side. One way of making structures lighter is to put empty plywood boxes inside of them. For example, to get a carefully sculpted tower on top of a tall structure, the tower can be built over a plywood box and lifted to the roof when it is finished.