Boxes for moving, shipping, and packing are more complicated than you think, and choosing the wrong box for your project can result in damaged belongings, wasted money, and interrupted storage. Several factors will determine the type of box you use for your storage project. Here are just a few variables to consider:

• How big and heavy is/are the item(s) you plan to move? If your items are large and/or heavy, opt for a sturdier option. If you’re able to estimate weight and size in advance, you can buy a box perfectly suited to your needs.

• How long will your items remain in the boxes? If you’re planning for a long-term storage option, sturdy boxes are the way to go. However, if you plan for items to remain in boxes for a month or less, a cheaper, less sturdy box will keep your belongings safe.

• How much are you willing to spend? This is perhaps the most difficult question of the bunch. While it might seem like a better deal to grab that free box behind your grocery store, it won’t last very long. More often than not, it will be damaged during a longer move. Used boxes are rarely good, regardless of their appearance—they are likely to have already suffered some degree of damage.

So, what constitutes a sturdy box? The difference between boxes comes down to one major factor: the number of walls. A single-walled box will have just one layer of cardboard, whereas a double-walled box has two layers for added stability and durability. Most standard moving boxes are single wall, as they’re meant for one-time quick use. More storage boxes are double-walled, as they’re designed to handle heavier loads and longer storage period. If you’re planning to store belongings for an extended period of time, I’d say that double-walled boxes are well-worth the extra cash. You can buy them at Home Depot, UHaul, The UPS Store, and Walmart.

If you want to take your chances with a used box, you can get them from Walmart, Target, Barnes & Noble, the local liquor store, or a similar business toward the end of the day.