Some women wait years for their turn at the annual Running of the Brides, where designer bridal gowns can be had for a fraction of retail. This year, with the usual location—the original Filene's Basement—under construction, the sale is slated for 8 a.m. on 2/22 at Hynes Convention Center. The begging, bartering, and grappling for labels like Carolina Herrera and Vera Wang, however, will be as ferocious as ever. To make sure you don't risk a trampling for the wrong dress, Boston wedding gown designer Ana Hernández shares tips on what sets the knockouts apart from the knockoffs.

Label As a general rule, the costlier the gown, the better the construction—until you reach $5,000. After that, the difference in price comes down to the designer name on the tag. Hernández, whose dresses top out at $8,000, gets her materials from the same supplier as celebrity fave Monique Lhuillier, whose bridal frocks can command up to $18,000.

Size The majority of the designs at the Running of the Brides come in sample sizes of 8 or 10, so smaller-framed women could end up paying as much in alterations as they would for a new dress in the right size. To make adjustments easier on your seamstress, look for a simple strapless gown without heavy beading or lace, and an unadorned bottom hem.

Lace Most high-end dresses use one of two types of lace: light and airy Chantilly and embroidered Alençon. Both are heavy enough to lie flat, but are soft to the touch. By contrast, a less expensive lace made from an acetate or polyester blend will feel crunchy. "You think people aren't going to touch your dress, so they won't notice," Hernández says. "But then they hug you, and really feel the quality of the gown."

Embellishments Choose your bling wisely. Swarovski and other glass crystals are nearly invisible when you look at a dress straight on, but they reflect light when you move. Plastic beads, on the other hand, usually require a much heavier application for the same amount of sparkle.

Weight Because they don't require fusible interlinings or underpinnings, heavier silks like this peau de soie create a smooth silhouette. But different patterns call for different fabrics: A Carolyn Bessette–style bias-cut sheath should be made of a lighter silk georgette, while a gown with ruching at the top works best in silk taffeta or silk duchess satin.

Fabric While natural fibers like silk and cotton may scare off wrinkle-averse brides, they breathe better than synthetic—and are lighter, too. "If you pick up a dress that looks like it weighs 20 pounds and it weighs 3 pounds, those are natural fibers," says Hernández. "If it really weighs 20 pounds, that's polyester or acetate—it's like plastic. You'll be sweating the whole time."

Silk mermaid dress with Alençon lace overlay and Swarovski crystals, $4,200, Ana Hernández Bridal Salon, 165 Newbury St., Boston, 617-536-2500, anahernandezbridal.com.