Sales of bulletproof backpacks have spiked almost 300 percent following a spate of school shootings and the recent attacks in El Paso, Texas, and Dayton, Ohio. Yet, none of the backpacks currently on the market would have stopped a single rifle round coming from those gunmen.

Bulletproof backpacks and backpack inserts for students are for sale online and on the shelves at major retailers including Office Depot, Home Depot and Bed Bath and Beyond. Made by companies such as Bullet Blocker, Guard Dog and TuffyPacks, the backpacks sell for anywhere between $99 and $490.

“It's sad that we even have to consider a product like this, but it's the issue that we have to deal with now and hopefully we won't in the future," Steve Naremore, CEO of TuffyPacks, said.

What makes these backpacks bulletproof is a back panel or an insert made of a flexible ballistic fiber material that the manufacturers market as having been independently tested up to the same standards as National Institute of Justice “Level IIIA” body armor for law enforcement.

Mollie Timmons, a Justice Department spokeswoman, said that the institute — the DOJ's research, development and evaluation agency — does not test or certify the inserts or the backpacks themselves, and that "marketing that claims NIJ testing or certification for such products is false."

To block the kind of piercing ammunition frequently fired by military-style rifles in recent mass and school shootings requires protection containing a hard ceramic or metallic plate weighing several pounds, with a “Level IV” rating.

The efficacy of bulletproof backpacks being marketed to students and parents was put to the test by Scott Reitz, a firearms instructor with the Los Angeles Police Department, in a demonstration for NBC News Los Angeles.

The “Guard Dog Security ProShield II” bulletproof backpack, rated Level IIIA, was mounted to a mannequin torso in a t-shirt and placed on a firing range.

Reitz fired at the backpack with a 9 mm pistol and with a .45-caliber handgun.Both shots penetrated the backpack’s exterior and inner fabric, but were stopped by the back panel armor.

Then, Reitz fired two shots from an AR-15 rifle, the civilian model of the U.S. military's M16, used in some recent mass shootings. Both went completely through the back panel and, with a flicker of the shirt, exited the mannequin’s back.

Simple physics explains how the bullets went through the bag.

“Rifle projectiles present a threat level greater than handgun and even shotgun ammunition," Peter Diaczuk, professor of forensics at the John Jay College of Criminal Justice, said. "This is due to the higher velocity and consequently greater kinetic energy of a rifle bullet.”

Yasir Sheikh, president of Skyline USA, which makes the Guard Dog backpacks, said in a statement to NBC News, “When considering protection against rifle round ammunition, that entails a thick, heavy ceramic plate which is not practical for daily carry use, especially when considering a child or young adult. Our backpacks are rated for Level IIIA, which is often the same protection used by local law enforcement.”

Despite the lack of protection against rifle ammunition, Diaczuk and other firearms experts don’t have any recommendations against using the backpacks.

“If I were sending a child to school, and the extra weight of the ballistic panels were not a burden, I would favor the protection,” Diaczuk said.

Almost 40 percent of adults say they’re “very concerned” about a shooting at their kid’s school, according to a new Morning Consult poll commissioned by NBC News. And almost half of adults say they would buy a bulletproof backpack for their child.

John Drury recently bought a bulletproof backpack insert for his son, Peyton. They live about 45 miles from Dayton, Ohio, where a gunman killed nine people last week.

“I never would have to walk around with a bulletproof backpack to feel safe in school," Peyton said.

Drury says the backpack’s price is worth the peace of mind.

“At the end of the day, I want my son to be able to come home from school,” he said.

CLARIFICATION (Aug 30, 2019, 12:45 p.m. ET): Although bulletproof backpacks have recently been for sale on Walmart’s website, the retailer says it no longer sells the backpacks, and those now-removed listings were from third-party companies selling through its online marketplace in violation of Walmart’s policies. The company has been removed from the list of retailers selling the product.

CORRECTION (Aug 30, 2019, 4:35 p.m. ET): A previous version of this article misstated that a back panel or insert for bulletproof backpacks had been rated by the National Institute of Justice. Neither the inserts nor the backpacks themselves are tested or rated by the institute; it only tests body armor for law enforcement.