Whenever there's a school shooting, sales of one particular item surge due to worried parents.

Earlier this week, 17 innocent people were killed in a Florida school when a former student opened fire with a rifle.

It’s the 18th school shooting in America in 2018.

Whenever such an incident takes place, there’s one particular product that sees a surge in sales thanks to parents.

Bulletproof backpacks.

It's a product that shouldn't even have to exist, but unfortunately in the world we live in today it's necessary.

And as a country - and a world - deals with the news of yet another shooting, thousands of parents have their fingers hovering above the purchase button.

According to TMZ, Massachusetts-based company Bullet Blocker sold 500 of the backpacks on Thursday alone, the day after the attack. The majority of those were going to Florida.

Founder Joe Curran, a former law-enforcement officer launched the company 11 years ago after the Virginia Tech massacre. He had two children in middle school who he wanted to protect.

"I had some old bulletproof vests kicking around, and I cut them up and stuffed them in their backpacks. I told them, ‘If something happens, hold this between you and the guy with a gun and hunker down behind it'," he told The Cut.

Guard Dog Security is a Florida-based company that also sells bulletproof backpacks. President Yasir Sheikh started selling then five years ago after 26 people - including 20 children - were shot and killed at Sandy Hook Elementary School.

He told The Cut sales of the backpacks had been "consistent' but that they also generally see a spike after mass shootings.

Listen: Why is Trump refusing to talk about guns? Post continues after audio.

Due to customer demands, these backpacks look like any others at first glance, available in bright colours and patterns.

Inside they are made using Kevlar, a bulletproof material that's reportedly five times stronger than steel. As well as help protecting, they can be used as a shield.

Compared to your standard's kids backpack they are not cheap, with prices starting at $250 and going right up to $620. They are prices that not all families can afford.

Parents are also split about whether they are a good idea, with some believing it's unnecessary or would cause more upset or trauma for children when explaining why they need one.

What do you think? Tell us below.