Can the humble park bench be considered hostile? Seems like a silly question.

But for some of the most vulnerable people, the design of public furniture can mean the difference between them feeling safe or not.

Experts say the shapes and designs of seating in the built environment are becoming increasingly hostile and homeless services say it's one way vulnerable people are being pushed out of cities.

It could be a curve in its design, sharpened edges, or arm rests placed in the middle of the seat.

They are details that make it uncomfortable or impossible to sit for a long time or lie down.

It's commonly referred to as hostile architecture.

Len's struggle

For Len James, these design features made the daily battle of finding somewhere to sleep even harder.

He became homeless on the streets of Perth at 58, after a back injury put him out of work.

"In a subtle way they let me know that they didn't want me there, so I had to look for somewhere else," Mr James said.

Mr James is now in social housing but he said feeling rejected by his city sits vividly in his memory.

"When your world becomes very small, things are exaggerated, so these things weigh heavily on you," he said.

Hostile architecture isn't limited to the design of benches.

High-pitched ringing in a stairwell, music playing on loop or sprinklers coming on in parks are all ways people can be told to move along.

Creating barriers

Regional Urban Planning Lecturer at Curtin University, Shane Grieve, said these design features are intentional.

"[It's] all the little design elements that we put into what could be commonplace architecture that actually makes it difficult for people to be there for much longer than they should," he said.

"The 'should' is determined by somebody else."